In my opinion, I'd have to sy Raiden. After using him in Arcade, I never touched him again. I just don't find him fun to use -- at all. And it's not because he's a combo character -- I had fun during my Dante days -- he's just kinda stale. There's nothing about him that stands out except his easy confirms.
I don't like his design, I don't like his voice, I just don't like Raiden!
At least his background is nice -- it's still my fav.
What about you?
Heihachi. He's got a horrible level 1 (I don't KC by the way), and his level 2.... I don't know, kind of boring to be honest. All you really do is run around while watching Kuma kill everyone (not to mention Kuma can also be pretty retarded sometimes lol). I like his level 3 cinematic, but it's not really worth it considering you can only get 3 kills max. Also, Heihachi's moveset is very plain. Pretty much just different variations of punches and kicks. Nothing special.
Fat princess , I used to have a lot of fun with but now she's just god awful to use, her needed air forward circle is terrible because it takes too long attack leaving her to be pretty much a flobby punching bag. Most player I see using her just do nothing but bounce-a-round!
Add the user Got_MILF93. Play his Fat Princess, and may the gods be with you. 0_0
Most characters are really fun to use IMO.
However, the characters I really can't use are Sackboy and Sly. Their gimmicks are just unappealing to me :/