I've only put about 15 hours into the game so far, so I'm still not entirely sure who I will main:
Previous main: Link
Verdict: I just plain don't like him anymore. While some aspects of his game have been improved, a lot of it has lost its appeal (to me).
Previous main: Bowser
Verdict: A near opposite of Link, I love this Bowser much, much more than his Melee incarnation (though I loved him before, too). He's slightly faster, more durable, and MUCH better looking. All in all, if there is any character on the roster that calls my name right now, it is Bowser.
Current interest: Falco
Verdict: There isn't much to say here. I'm a fan of the Starfox series, but the characters didn't really appeal to me in the previous games. This time, however, Falco has definately caught my eye, and I actually have fun playing as him.
Current interest: Meta Knight
Verdict: My sentiments are really no different from anyone elses on this character. He's cool, and he's fun to use. In the end, I'll probably use him quite often, but he'll be one of those characters that I internally spout profanities at for a lack of power moves. Though, I have found that he is a beast in the air, especially off-stage.
Current interest: King Dedede
Verdict: I'm pretty torn on Dedede. On one side, he's a character that I really like, and he plays fairly well. But, aside from projectile spam and chain-grabbing (even though it's a lot), I don't really see what he has above Bowser. Maybe I'm just biased, seeing how Bowser is my favorite Nintendo character. Either way, I like him, but he isn't anything extraordinary.
Honorable Mentions: Ike, Snake, and Luigi
Verdict: These are basically characters that I will pick up every once in a while but mosst likely not devote any real attention to.