Budget is a big player in knife selection, closely followed by function (steel types, single/multi-purpose, locking and deploying mechanisms), and "fashion" for lack of better words. Figure out what you need it for, be it as a cutting tool, rescue, defense use, prying, or otherwise. I stay away from cheap knives because while they may cut well, I've found their liner locks to be weak and dangerous.
State laws as well play a huge roll. Check them before you go buying, especially for length, function and purpose. I can "go armed" for self defense with my Glock in Tennessee because I have a CHP, but heaven forbid if I do it with a pocket knife, so I'm in search of something less aggressive looking just to reduce the odds of playing the legal game. Idiots...
There's a lot of good options from Benchmade in the <$100 category such as the Griptillian and Mini Presidio, and higher grades of Benchmades along with Emersons, Tops and many others in the $100-$200. From there you can start really going all out for a Chris Reeve, Spartan Akribis, Rick Hinderer, or straight custom if you want to drop some more dough on a fine piece of craftsmanship. Search for the deals on the Benchmades, and I buy mine from Knifeworks.com as they have the best prices on the net with the discount code "BR549" and a huge inventory and selection. Even Benchmade's Promotive store can't touch Knifeworks.
What I carry at work is a Leatherman Wave, combo edge folding Benchmade 581 and a short fixed blade Blackhawk Crucible with a combo edge. At home I alternate between an Emerson SOC-FK and a CQC-7, but I really want to get a Sebenza for daily carry. Dang gun builds keep getting in the way of that budget.