You've asked the $64,000 question. Here are the answers you'll get:
1. SAK "It was good enough for my dad, it's good enough for me. Oh, and the corkscrew looks cool."
2. Sharpened Prybar "You never know when you'll have to pry apart an abandoned bomb shelter to get to food."
3. Scandinavian knife + axe "A knife is made to CUT, not PRY, and if you are very careful and don't do stupid things, my puukovestalita at Rockwell 70 will outcut anything short of a lightsaber. The axe is for chopping."
Your question oversimplifies the issue, really. You can get wafer-thin 6" scandinavian blades, or Busses that are 4" long and 5/16" thick. A SRKW Battle Rat (9"x1/4") is a hell of a chopper, but heavy to carry up mountains. My armchair recommendation would be as follows...
1. Quality locking folder 3"-4". You can do all of your small knife tasks with this.
2. 7"-9" chopper, beefy. You can do all of your big knife tasks with this.
3. Multi-tool. All the little gadgets that an SAK has, but generally more robust.
As for self-defense/camping knife...well, I don't have any knife fighting training, but as I understand it each type of knife has different requisite qualities. The Chris Reeve Green Beret knife is supposed to be a heck of a fighter, but relatively brittle and not balanced right for chopping, thus a relatively poor camping knife. If I were you, I would lean heavily towards buying a good camping knife, as you're going to be doing a hell of a lot more camping than defending yourself.