Both outstanding knives for very different sorts of use. My BK-2 is a sturdy, hardy tank of a belt knife. It works fine for cutting my food, chopping, splitting (within reason - the blade is only so long), bonking things on the head (I hunt rabbits, squirrels, deer, etc.) when needed and so on.
The 110 I used to have (sadly no more) was great for cleaning game (though it needed cleaned quite a bit afterwards), opening packages, cutting my food and fitting in my pocket.
I guess if I was bound and determined to buy one and only one of these two, it would be the BK-2 because I expect it to outlast the Buck and there are things I can do with it I wouldn't try with the Buck (though I can't really carry it in my pocket to work and so forth).