The above poll would seem to indicate that it is Krystal who comes out ahead.
The easy moveset, the fact she is THE most scantily clad woman in nintendo history, (Kongs dont count- they don't have anything to cover in the first place) the GF connection, her storyline presence in Adventures and Command.
When you get right down to it, Wolf was originally nothing more than a Miniboss. If someone had suggested him for Smash 64, he would have been laughed off as no more qualified than a Chozo Statue. (The statue at least had moves...)
Adventures came and introduced Krystal, and set her up as a major romantic interest for the hero.
Assault scaled back Krystal's role (while keeping the GF angle) while bringing Wolf center stage. All the cool Wolf art comes from this one game, and they even made him playable in vs mode. It is also widely considered the worst Starfox title to date.
Command, from what I've read, buts Krystal back in center stage. Star Wolf are a major part of the plot, but the Fox/Krystal relationship is what drives the story.
So, Krystal has been central to the plot of 2 games and had a suporting role in a third, wereas Wolf was central to one awful game, (Assault) was a miniboss in another, (64) and was a supporting character in a third.