Some of my rankings don't veer too far off what's been posted already but there's one in particular I just had to post about.
Marine - 7. Actually, she was somewhat disappointing considering how she's a one-woman army during most of the rest of the series. It mostly depended on Jeanne's hints and how cryptic they were for some of the opponents that had an edge.
Benoit - 5. Even with his slow start, he tended not to do too well in most matchups and was easily tricked.
Karine - 9. Definitely the second best character as far as reliability was concerned because she could be counted on to beat just about anyone.
Hirado - 6. Despite being statistically one of the best characters at level 99, he was tricked often and seemed not to do much damage due to misses or incompatible attack types.
Abu - 4. Speaking of disappointments, Abu was one of the most easily tricked characters and didn't fare well in other bouts either.
Jezabel - 7. Considering how awful she is in most of the series compared to the rest of the 13, I was surprised at just how effective she was (almost solely due to that amazing match-ending kick).
Jack - 1. Statistically he's the worst of the 13 in almost all the categories and he plays out that way in the showdown too. I suppose with tricking he could potentially be more useful than Wolfgang but that's just because of how awful Wolfgang is...
James - 5. Females in particular had him tricked to a fault, but in fights without tricking, he tended to do well, at least until he ran out of special attacks, at which point even his wolf hat wasn't good enough.
Salome - 8. Sure, she hit extremely weak and could only fell a few physically. But that isn't where she shines - all but two of the primarily male opposition fall to her tricks with a VERY high percentage, and even one of those exceptions falls for her wiles from time to time.
Wolfgang - 1. He MIGHT take down an enemy or two with special attacks. For the most part, he's only good at losing.
Bokden - 8. While he's better at Karine in fighting, he does get tricked, which makes him somewhat less useful in the showdown.
The Bear - 10. When it's almost impossible to lose a match (though the dialogue is PRICELESS when he does) and even Lord Dragon isn't even close to scratching him, you pretty much know why everyone wanted (or hoped he wouldn't in the case of the enemy) him on board.
Old Suzuki - 8-9. I didn't quite get the hang of his tricks but near as I can tell, he's pretty much one of the best fighters regardless of whether you do typical fights (primarily because he seems to dodge better than anyone in the showdown, despite having lower speed than a couple fighters) or know what trick moves to use. Considering everyone considered him a joke, it was poetic justice!