I found that blades up to 4" are my preferred size. So far they were up to every cutting job. I even use them for dressing game. On a special occassion I had to butcher 5 wild boars (about 100 lbs each) that were killed in a collision with a car. The 4" blade was entirely up to the job. I only carry a larger blade when I know that I´ m going to need it.
I severely lean towards the fixed blade as many other posters here. The fixed fixed blades are simply more robust and can be kept clean much easier. For camping or survival keeping the knife clean can be a health issue. As carry my folders in a belt pouch lint isn´t really an issue. I carry the folders to work and in urban environment. My EDC fixed blade has a 2" blade and fits nicely in a front pocket of my vest (redundacy can´t hurt).