Quite obviously late to this party (so late that it looks to be over actually), but I cannot resist my attempt to answer "THE Question." Any discussion about knives, let alone Busses, always seems to end up leading to this one question.
Lots of great knives listed, but I think one has to define the parameters of "the one knife" question.
If the point is simple, pure pride and pleasure of ownership/possession, then sure, one can go with the one knife that gets ya' goin' the most - Battle Shark? Huck Finn? MOAB? Shiva Rex? (why not small?) - whatever floats your boat the most.
But if the question is what is the one knife that you would pick if you could only have one for general survival or wilderness use, then the answer might be very different. It might be a knife that doesn't even get your knife collectin' juices flowing in the slightest, but on a practical level presents the best "one knife" answer.
Me? I am most attracted to knives that provide a good potential answer to "the knife, if only one, for general survival/wilderness use?"
For me the answer is ASH-1 all the way (pick your flavor - they are all good)! (runners up: NMSFNO and HOG Badger - can't go wrong with either of those as well!)