The answer to your question is my 10" K-Sabatier chef's -- for its combination of edge qualities, versatility and toughness. But your "one knife" hypothetical is so much about those three qualities -- especially toughness -- the answer was a no-brainer.
But, it is not the knife, not even the chef's knife, I use most often. When choosing one knife to use to cook a meal, it's usually either my Konosuke 270mm gyuto (chef's) or Konosuke 300 suji (slicer). In my case, they are nearly interchangeable, but wouldn't be for very many other people. More, long, expensive and flimsy knives like the Konosukes, which put a premium on board size as well as knife and sharpening skills, aren't the best choice for everyone either.
N.B., I mention the brand only to highlight their "laser," and slightly delicate natures. That is, neither would be an appropriate as an "only" knife which might run into bones or very tough fruit and vegetable skins and stems.
The answer to the question to which knife I respect most, is probably the Konosuke suji because of its very surprising agility. Even at 12" the blade is both very light and ridiculously easy to point. Plus, the handle makes "coming over the top" very easy and the knife has just enough shoulder to make chopping a breeze -- as opposed to most slicers which are real knuckle smashers. It's not really mo' bettah than the gyuto though, just newer.
Fortunately, I have more than one beloved knife and hope you do too.
Finally, the practical answer to most knife choice question lies more in sharpening than elsewhere. Almost any sharp knife can perform almost any knife task better than almost any dull one.
BDL
Edited by boar_d_laze - 7/5/11 at 6:20pm