There will not be an official tier list for a while. Tiers are mostly based on tournament results, so after about 1 year we will have an accurate list. Of course no one will wait that long, so someone will end up making a list as soon as they get the game.
Speedy characters are usually high on the list, so they have an inherant advantage, but Brawl seems very balanced. Heavy chars like D3 have a chance at high tier because of super armor. I bet the tier list will not affect high-level play as much as it did in Melee.