Sm4sh: Most likely going to be unbalanced, closer to brawl than melee, and sakurai already said he hates competitive smash, also is probably going to take forever and I'm going to have to drop 400 dollars on a wii u first.
Brawl: Don't even get me started. Has horrible physics, the world's worst matchup spread, pratfalls, meta knight, tries its hardest to limit competitive play and limit the player's exploration of the depth of the game
Melee: despite having the best physics of any smash game, is still incredibly unbalanced, has few viable stages, and the metagame is full of annoying melee fanboys
64: lol
project m: combines characters of brawl with melee physics, depth, and tech skill, brawl graphics, and the best stages made throughout all three games. Is actually balanced, with all but one character being competitively viable (come on DDD). That's so far, the game is constantly being improved by a group of devs who understand the metagame and actually listen to the players, unlike sakurai. I have more vested interest in p:m than any smash game, and sm4sh won't change that unless it's the same as project m, except with villager and megaman. Which we already know it won't be.