Tbh, I'd rather put in the work to improve in Melee or B+. I'm a fairly vain person, and I like for improvement to literally be visible. Improving in Brawl stops to look significantly more impressive immediately after the point in which you no longer commonly make technical errors. It doesn't stop getting fun to play (without some Melee, B+ or 64 breaks lol) though, and it's still exciting to notice improvements in prediction, spacing, or matchup knowledge, which are really the only areas where it's possible to improve in Brawl.
Just like I really wouldn't want to split myself by choosing multiple mains, since I feasibly only started taking Brawl seriously about a half year ago, and Melee and B+ a little more than a month ago (though I have learned an immense amount of information regardless), I would really like to fully devote myself to improvement at one game.
In the meantime, since I do not see much competitive potential in Brawl, I will learn Metaknight, for no other reason than his high learning to ****** ratio. He's actually really fun to play too, surprising. I thought it would get old to gay people to death over and over and over again, but it really doesn't.
EDIT:
@Uncle: Bro we still have to team for the next Stacks man. I'm freaking excited for that shiz.