4:20 p.m. on September 14, 2012 (EDT)
of course, it depends.
quality is something that will draw a diversity of opinion, depending on a person's likes/dislikes. ultralight hikers will usually choose the option that hopefully gets the job done at the lightest possible weight. people who don't want to spend a lot of money will tend to choose the least expensive option. my bias? i don't like throwing things away or replacing them, and i hate it when i'm out hiking and something fails. i'll spend more on something that i think will last a lot longer. in knife terms, i would rather spend a little more and get a knife that i'll use for a really long time, & that i don't have to sharpen often.
as a preface, on most trips of any length i take a multitool and one knife. for a long time, though, the smallest/lightest/cheapest knife i carried was the Opinel #6. folding knife, wood handle, steel blade with a ring that twists and locks it. cost me a few bucks and was fine for several years. you could buy one today for 10-12 bucks, I'm guessing. i took a fresh look at knives after i accidentally sliced my thumb open with that Opinel, though. slippery handle, and i was trying to pry something with it. of course, i blame the knife rather than my own stupid behavior. of course, it's the better handles on my current knives that have avoided repeated mishaps, not the fact that i learned the hard way to use knives the way they are supposed to be used. :)
i think some sort of multitool is extremely helpful in repair situations. i have used pliers to repair external frame backpacks, snowshoes, crampons, trekking poles, tent stakes that get bent. i don't know if it's necessary, but it is pretty darn helpful.
that same multitool could be used to prep meals, gut a fish, whittle a branch into a makeshift tent stake, fuzz up a stick to help start a fire, cut webbing or rope. for most people, then, a multitool could render another knife unnecessary. Most people who have used the knife on a multitool for an extended period of time know it isn't very comfortable in your hand & can take a bit longer, or a lot longer, to do whatever it is you are doing.
knife blades shorter than 2 inches don't make a lot of sense to me, or they end up being too small for doing even basic things. on the other end of the spectrum, i can't recall any situation where i longed for a knife blade longer than 4 inches.
i don't always know why i'll take one knife vs. another on a trip, but i'll give it a try.
1. handle comfort - if you don't end up using a knife much, it doesn't matter much. if you do, if you have a habit of whittling things, choose one with a decent handle. example: kershaw makes a small folding knife called the chive that has a blade about that size, it's very small folded up. weighs about 3 ounces. the blade locks open nicely. it isn't the greatest knife to hold while doing anything heavy or extended because it's so small, but it is fine. it's not cheap, considering how small it is. in contrast, bark river knife & tool co. makes some small fixed blade knives, the PSK is one example. same blade length as the chive, but it is a fixed blade knife, has a thicker blade that is much less likely to get damaged, it stays sharp much longer with regular (or irregular) use, and has a much more usable handle. weighs a little less. it's quite expensive for a small knife; other companies make similar knives for less, i'm sure. independent of price, i'll take the one with the better blade and handle. all things equal, i think the handles on knifes with a blade in the 3 1/2 to 4 inch range are more comfortable in my hand than the smaller ones - that's one man's opinion.
2. composition of the blade - i have one knife that has a carbon 'tool steel' blade. i won't use it if i expect really wet conditions or plan to be camping & using it near the ocean, the steel doesn't handle those conditions well. otherwise, it's a great knife. also, for river rafting in particular, it's pretty important to have a blade that doesn't have a pointy end, and can be pretty important to have at least a little serrated portion of the blade.
3. fixed vs. folding - mostly, this is a function of how dirty/messed up the conditions are where i'm using the knife. if i expect something to get really gunked up, i'll take a fixed blade. they are uniformly easier to clean than a folding knife, and taking apart a folding knife to fully clean out junk is a PITA. still, unless you have a very small fixed blade knife, you probably aren't going to walk around with it in your pocket and may not feel it's convenient or socially acceptable to walk around with the sheath on your belt or pack. i'm much more likely to bring a folding knife based on the company i keep, if having something long and in a sheath will be off-putting for some reason, where a folding knife can just sit in your pocket or unobtrusively clip onto your pack straps or pockets until you need it.
4. how you carry it - relates to what i just said, but with a few wrinkles. folding knives can be much easier to carry around because they can either be in a pants pocket or often has a spring clip & can be carried on a backpack strap or pocket edge. special situation? if you're rafting or canoing and want easy access to a knife for some reason, you will want one that's shor tand has a sheath that can attach to your PFD. knives with spring clips have a funny habit of knocking loose and dropping into the river when things get hairy; knives with a belt sheath can get in the way when you're paddling or sitting in certain ways.