I'm not going to claim to be a great player, but I have owned and played the game since the day it was released so take these predictions with a grain of salt. Anyway here is my take on a few of my preferred characters.
Jigglypuff: I know she has basically been nerfed a bit since Melee, but I still feel as if she is undervalued and that she has strong matchups against the rest of the high and top tiers.
Luigi: Reasonably fast, good KO moves, a good final smash, and a balanced air and ground game make him significantly better than he was last time around, and a general improvement over mario, who is still middle of the pack.
Diddy Kong: I keep seeing tier lists with diddy at rock bottom and I can't help but wonder what people are thinking. His air game is great, he has a solid recovery and some nice spikes, a good projectile, and he has amazing combo potential with his bananas (among other things). To top it all off, he is one of the few light characters with massive KO potential.
Wolf: I can't help but think wolf is overrated. Good? totally. The best? No way. I see so many people talking about wolf as if he is imba and number 1. Frankly, brawl is very balanced, and there are alot of other top tier characters who can stomp wolf into the ground. That being said, his fsmash is EASILY the best in the game, he has great air combos, and his laser is a good projectile. His recovery is mediocre, but everything else is pretty solid.
Young Link: My pick for the current #1 spot. Best dair in the game, decent kill potential, great projectiles, fast as can be, good range, good recoveries, amazing combos, he pretty much has it all. The only chars I've had trouble with when playing ylink are G&W and metaknight, but I imagine a good dedede would give me problems too.
Marth: Basically the same as melee. Some points are better, some points are worse. Most marths I've played against in RL are button mashers, so I would imagine that he will attract more of the same this time around, but he is far more powerful in the hands of someone skilled.
Ike: The new favorite of people who wish slow powerful characters could be worth a ****. Poor them. That being said, he is a blast to play as a "messing around" type character.
Olimar and Pikman: I've had alot of fun with Olimar. He has great smashes, great projectiles, and alot of variety and fun. His recovery is about the worst in the game, and his complexities are numerous, but I predict that as he is picked up and learned by more and more top players, he could become a major presence in the competitive scene.
Sonic: Brutally fast movement and some fun combo potential. For me, his "roll into a ball" attacks are annoying to play, but I'm guessing he will get picked up by alot of people looking for speed.
Kirby: Wow, talk about a change. Kirby is faster, more powerful, and more versatile. Fun to play as, and he has alot of potential, but I don't see him any farther up than lowish high tier.
Snake: My pick for best final smash in the game, and he has a pretty cool style of play. Very stealthy and technical. Also requires a big attention span, what with all the mines and whatnot. Could be great, could be passed over and forgotten for competitive play. Either way, he has the possibility of becoming a tourny staple.
Pikachu: First off, let me say I don't play pikachu, but I play against them in my smash groups all the time. The brawl pikachu is terribly annoying, and its tower of lightning is horribly, horribly annoying, especially when playing a heavily aerial character. Faster this time around, and with great recoveries. Could be decent tier wise.
Anyway, those are my current assessments. I'm sure these are nearly all wrong, but hey, I had fun testing the chars out and posing my results, so, hey