I don't see how anyone's supposed to have a decent answer for this even unofficially when the game hasn't been out for a month yet. I don't think I've even worked out my "official" best and worst characters in Melee, and that had 13 less movesets to choose from and six more years to decide.
Anyway. I will main Jigglypuff; this will not change unless they ruined her in every way. That doesn't make her my best, just my main. Kirby and Meta Knight will be co-mains; I like flying characters, if you can't tell. Zelda, King Dedede, Captain Falcon, Ice Climbers, Luigi, Ganondorf, Falco, and Pikachu are all pending how good I am with them. Note that King Dedede's the only fully unproven character there--I'll stick with the others as long as they haven't been too nerfed from Melee. Might play Sheik a little too, just because I like Zelda. I like the unorthodox movesets for Ness, Lucas, Mr. Game & Watch, and ROB, but they've got a lot to prove. Ness and G&W would have to be buffed. Lucas and ROB I can't speak for because I've never played anything like them.
Meanwhile, I'll never use Donkey Kong, Yoshi, Wario, Link, or Fox unless random picks them for me. (And even then I just might reset instead.) Don't like the personalities of DK, Link, Fox, or Wario, so whether Wario is good is irrelevant to me; I won't be playing him either way. I do like Yoshi as a character, but I've always sucked with his playing style. I'll probably also pass on Mario, Samus, Bowser, Pit, Zero Suit Samus, Snake, Ike, Diddy Kong, Sonic, Olimar, and Lucario unless they prove to be a lot better than I'm expecting.