I guess it would depend on terrain, intended uses, duration of trip, and what other gear might be brought along. For instance--if I an axe will be coming, I'd probably opt for something smaller. If no axe, and I'm going to have to depend on the knife, I'd probably bring a larger 'chopper.' Am I going on an 'overnight' with probably little knife usage or a week trek through the forest where the knife will get used alot?
All in all, if I had to pick one, I'd probably opt for 5-7 inch heavy duty, preferably drop point. A SwampRat M6, CRK Shadow IV/Project I, something along those lines. Many decent choices.
FWIW, I seldom carry only one. I usually have fixed blade, a folder, and/or SwissArmy/Multitool. Can't be too prepared...
In the end, w/ decent gear, it'll be the operator, not the tool, that makes the difference.
BOSS