UPDATE 11/17/08: I've had some new ideas and changed opinions since I've written this. If you enjoy this post, please take the time to read More thoughts on choosing an EDC knife
Many people have asked me what kind of knife they should buy, and I've always answered in the same way, "it depends." Well, that was kind of a cop-out answer because I didn't have/take the time to go over all the qualities you should be looking for in an EDC knife. Well, here's my definitive answer to that very question.
In the following paragraphs I will go over the qualities that I require from an EDC knife. In reading you will also find my definition of an EDC knife, should you be confused about what should be required and expected of an Every Day Carry knife.
Should you wish to bypass all my conclusions, you can skip to the bottom of this post where I make a recommendation for an EDC knife that will probably fit most people and their uses.
Always remember: all knives are not created equal. You've probably seen a lot of knives in your life, and either think you know a bit, a little bit, or nothing about them. Don't make uneducated decisions. Consult the internet as much as you can, and wrap your hands around all the knives that you can before making your decision. $30 knives have their place just as $200 knives do, find out what you need and don't be afraid of price. If you're in a reputable knife shop, it's pretty safe to assume that the expensive knife is expensive for a reason. Don't get into the trap of renting knives by buying cheap (though not always inexpensive) knives, and replacing them every year or two.
When some of you think of a pocket knife, the first thing you think of is your first "Swiss army" knife with a corkscrew (drunky!), bottle opener, and a blade capable of cutting soft fruit. This is not what I'm talking about. Your EDC knife should be a folder with a locking blade that can be rapidly deployed to cut people free in an emergency situation. The next time some kid gets his pants caught in an escalator you shouldn't be fumbling with that little thumbnail slot on your pocket knife/can opener/corkscrew/melon baller, your knife should ready and cutting before the kid's mom realizes what a poor parent she was for letting her kid sit on the escalator. Should you wish to carry a bottle opener, corkscrew or tools that are actually useful; I recommend you do so on another knife, or with a multi-tool of some kind. Sure, there are some tool-bearing pocket knives out there that satisfy a number of the requirements for an EDC folder, but there is no substitute for a locking blade that satisfies ALL the EDC requirements.
To me, partial-serrations are a no brainer. Your knife is for utility cutting, and serrations are deep, pointy, and retain their sharpness. Serrations will help you start a cut into thick material, and will tear into materials you wouldn't be able to cut with a plain blade. Sadly, your sarrations cannot be sharpened by most knife sharpeners, but if you're actually dulling your serrations (you know who you are), you're probably misusing your knife. I should note that I opted not to get serrations on my EDC favorite, and have paid for it on a number of occasions. Using a plain blade where serrations are needed qualifies as misuse. (doh.) Blade point is a matter of preference. My good friend has a knife that eats nails and shits razor blades, it's a large hunk of steel with a worn edge, worn serrations, and a tanto blade for strength. My EDC, on the other hand, is more elegant; it has a reverse tanto blade to ensure strength without sacrificing a curved blade for cutting ease. It depends on what you plan on using it. If you know you'll mistreat it (and some of you do) get a knife that'll take a beating. If you want it for some minor cutting here and there, get a blade that's quick to cut, and fast. Spear points (to me) aren't good choices for an EDC knife. Flat points are supposed to be for rescue type operations, but to me, you severely impair the ability of the blade by limiting it's ability to penetrate thick material. The non-cutting side of the pointed end should carry some of the thickness from the base of the blade to give some added security, should the knife be tweaked in a way that puts sideways pressure on the blade. Your blade should be forged from (at least) 440 steel keep a working edge. It should have 440 printed on the blade. I prefer the black coating on the blade because I think it protects the blade more than no coating does. And no, it doesn't make you a l33t super sniper ninja pirate spec-ops mofo to have a black blade, so don't even think about it. I actually prefer uncoated blades on non-work knives.
Here, I might get some people who disagree with me. I promote thick grips because thick grips fit your hands better than skinny grips. The grip is called a grip for a reason, you should be able to grip it! If you grasp a ruler, you'll find that it's fairly easy for you to slide the ruler up and down with your other hand. But if you grip a highlighter, you're going to have trouble moving it up and down in your hand. Don't get hung up on a slender profile, if it's uncomfortable in your hand, you don't have a sure grip on it, and it's not as functional as it could be. Your fingertips should just barely touch the strong part of your hand under your thumb, or be just short of touching it. The grip should not be like grasping a wooden pencil; that grip doesn't use the strength of the fingers in the grip. A clip is a requirement. The escalator is eating more and more of Little Timmy's jeans while you fish around in your pocket for the object of his salvation. Clips that place the knife in a downward facing position are preferred; it saves you the motion of flipping the knife around to ready it. I prefer wide clips to thin ones, as the wide ones tend to be looser without sacrificing tensile strength. I also find that the clip also affords a bit of girth, and friction which helps solidify my grip.
A stud on the blade is probably the most preferred opening method. It can be opened with a thumb-flick (once the knife is worn in), and doesn't require the thumb move very far from a gripping position. As opposed to a thumb hole which requires that your thumb move to a "thumbs-up" position to open the knife, which leaves your four fingers to be the only things holding on to the grip. The only choice in rapid deployment is the thumbstud. Auto opening knives that require only a button press to open are only slightly better than the thumbstud, but carry legal issues, and will make your coworkers wonder what the hell you're doing with a switchblade. I'd stay away from them for a number of reasons, but if it's legal, and you don't mind the stigma, feel free. "Flipper" style opening methods (a protrusion that sticks out the spine of the grip) must be opened with your index finger, and while reliable and effective, require your hand to be too far from a standard grip to be seriously fast. Note that you certainly don't need a lightening fast opening for standard tasks, and could easily get by with any of the other opening methods, but when you DO need it, you'll wish you had it. Is is advisable that you not to a wrist flip opening as it (usually) requires you to break the standard grip, and (usually) requires a recoil, a forward motion, and a flip back motion to open. This is just not as fast as a thumbstud, and attracts the same switchblade attention to you (while causing you to wave a knife around with a weak grip).
NOTE on thumbstuds: NOT all thumbstuds will allow you a thumb-flip opening! Try to get a thumbstud that is far from the pivot point of the blade. The farther it is, the easier it will be to flip open. When you're trying thumb-flips on thumbstuds in the knife shop, try to open the blade by pushing up on the thumbstud with the top of the end of your thumb-nail. Note that you probably won't be able to flick the knife open since it is new, and needs to be worn in. If you are able to open the knife easily by pressing up on the thumbstud with the top of the tip of your thumb-nail, you should be able to thumb-flick it once worn in.
I know I shouldn't have to get into this but pick a knife that fits the size of your hand! I know someone who carries around one of those obscenely long Spydercos! You should be able to wrap your fist around the blade without it poking out. Don't pick up something that doesn't fit your frame, you won't carry it, and if you do, you get into aggressive appearance issues (check the law section below). Knives are short for a reason, their strength is not in the how hard you can swing the blade like a sword, it's how solidly you can manipulate it with your arm and hand strength.
Your EDC folder must have a blade lock. Serious operation of a knife without one is dangerous to your fingers. I enjoy being able to unlock and close my knife in one motion, but that is not a requirement. What IS a requirement, is a lock that you feel is secure. I try to stay away from liner locks since they usually require a secondary lock to keep the liner lock from returning to a position where the blade is no longer locked. Why I'm locking my lock in place when there are other possible locking solutions is beyond me. However, liner locks allow pretty safe closing with only one hand, so it's really your call; maybe you like safeties on your safeties, it's a preference thing. One thing I won't abide, is a liner lock that does not stop against the center of the blade, and allows the blade to rock back and forth a few millimeters. If the lock is not firmly in the center of the blade, holding it in place, it is at the edge of the blade, holding it. A thin liner lock at the edge of a blade does not seem safe to me. Sufficient force could cause the blade to slip past the liner lock, and put your fingers in danger. Note that I don't feel the same about thick liner locks that may not lock right in the middle of the blade, but are thick enough that they reach the middle of the blade. The spine locks are very strong and reliable. My preferred locking method is the axis lock by Benchmade. The lock is strong and secure, easy to manipulate, and high enough that it doesn't interfere with the grip like other locks that use the side of the grips.
This shouldn't even be a factor. But if you're holding a knife, and find yourself thinking about how much it weighs; put it down. It's too heavy. A natural grip will keep the weight from being noticeable.
There are many laws that deal with carrying knives. It is necessary that you understand the laws for your state (and possibly city) before deciding on an EDC folder. Blade length is probably the most prominent one, but they're usually not unreasonable (well, considering there really shouldn't be regulations about this, I guess they're all unreasonable). Opening action is usually limited to the prevention of switch blades. Even in hoplophobic California, the fastest thumb-flick doesn't qualify as an automatic knife. We also allow switch blades with blades shorter than 2 inches (1 1/2"?). Auto-close became a big one a few years back, check to see that the knife "prefers" to remain closed. This means that if the knife is very close to being closed, it will go the last few centimeters by itself. I'm not sure why this was such an important legal issue, but it was. Aggressive appearance is an important one. This is your EDC folder, not your fantasy Klingon dagger of doom. Should you be required to use your knife in defense, a plain-looking EDC folder will look better in court than a double-bladed, spiney, black, etc... knife. When in doubt, just imagine the prosecution holding up the knife for the jury to see, are they going to gasp in horror, or have a surprised look on their faces? Or are they going to be underwhelmed and confused as to why the prosecutor is trying to convince them that this IS the dagger of doom? For the most part, you don't have to worry about what kind of knife you carry since most people folks don't care. Remember that if you go to a courthouse or other government property, you will be asked to relinquish your blade. In places like this, there are boxes (and boxes) of unreclaimed blades that folks have left there. Some of these guys have sticky fingers, so make sure you get a property receipt for your $200 knife before you hand it over to Bubba (or just don't bring it in the first place).
An EDC knife should be a folder instead of a fixed blade for one important reason. EDC knives should always be ready to go, and fixed blade knives are not always ready to go. Aside from being frowned upon (and illegal) in some areas (IE: everywhere but Texas :), they require a holster, and holsters require attachment apparatai. Belts, straps, hooks, etc, are all stuff you don't want to deal with, and probably won't when you decide whether or not to grab your knife before running out the door. With few exceptions, I always have a knife on me or within arms reach, and I wouldn't be able to do that if I carried a fixed blade knife (though I sure would like to be able to).
How long will it last? Does it come with a lifetime warranty? What materials is it made of? Will the blade rust? (it better not!) Does the handle look like it would shatter into a million plastic shards if it was dropped from 12 feet? Some of these questions can be answered by simply looking at the knife, or asking the knife salesman, but some of these answers can only be found through anecdotes and internet reviews. Talk to the knife salesman, ask if they know anything about the durability of the knife or if they get any returns of it. The easy way out of having to wonder about these questions is, you stick with a trusted brand name, and you actually pay a bit of money for it. All those quality materials aren't cheap, and won't come cheap. Spend the money now for piece of mind later.
Loose and tight, to me, it's all about loose, and tight. Tight is where different pieces touch. The tolerances should be extremely tight in almost every area. The only areas that should be loose are the clip tension (for easy clipping), and the area around the blade when closed. When closed, the cutting edge of the blade should NOT touch the grip in any way, this dulls the blade and smacks of poor craftsmanship. When closed the sides of the blade should not touch the sides of the grip. Inspect the hinge the blade pivots on, is it very well sealed? Open the blade slowly while inspecting the pivot point. Are there any burs or catches on the hinge? Or does it look like a solid, well machined... machine? Does it have cavities that stuff like pocket fuzz can get into? Like checking for durability, the easy way out is to pick a well known brand name, and spend a decent bit of money on the craftsmanship that comes with the name.
Should you consider your EDC knife an implement of self-defense, please read this post;
Dangerous Misconceptions about EDC knives
Should you be apathetic to finding your perfect EDC knife, I'll leave you with this excellent, average size, general purpose knife that fits the EDC requirements perfectly. My EDC. (except mine doesn't have sarrations, buy yours with sarrations) You should have no problem ordering one, should you live nowhere near a knife shop.