From what I played of the 3DS version (I just got it on Wednesday), I main different characters in comparison to the other games in the series. I mainly use Robin (Male or Female, doesn't matter), but I'm not really the kind of guy who posts lectures on combos and the like, lol. And oddly enough, I use regular Mario in this game even though I never bothered to use him previous games. I use Shiek and Little Mac every once in a while, too.
I dunno about that Wii Fit Trainer description though, the only thing I can agree on is that I predominantly use the female one.