Heh. This is a topic that I fear will never be exhausted. I definitely fall into the category of "why have only one when you can have two (or more). To answer the question more directly, my favorite all-purpose tool is the original Leatherman Wave.

But in reality, my daily kit consists of:

Victorinox Classic and Money Clip
Gerber AirFrame

usually, I will also have in my briefcase a Benchmade 100 River & Rescue knife, plus the aforementioned Leatherman Wave plus tool kit.

And when I hit the trail, there will also be a Benchmade 190 Drop Point Hunter and 192 Bird & Trout, plus a Gransfors Mini Belt Hatchet, unless of course, I've decided to carry some other pieces from my collection. The Gransfors is a permanent fixture, but the two Benchmades are my current favorite "hunting/camping" knives. I also generally carry a couple of Henckels kitchen knives for food (6" chef's and 4" utility/parer).