For serious competition, go with Melee.
If you actually play games for fun, and not for some stupid tournaments that require you to neglect 99% of the game's content just to play the same two characters on the SAME stage over and over and over without any of the elements that make Smash Bros unique to begin with. Then go for Brawl.
Besides, Melee is f*cking overrated as a serious competitive game anyway, it's crazy unbalanced, especially with all the abusable glitches. And for all the people who hate Brawl because it's more randomness than skill based and caters to more casual players, THAT'S THE ENTIRE POINT OF THE DAMN SERIES YOU IDIOTS!
That was what made the original Super Smash Bros such a great game, it was different from every other fighter out there, when Melee came around, it had more to offer for the so called "hardcore", but they pretty much ruined Melee by stripping all of the things that made the series unique just so they can do the same stuff they can do in any fighting game.
I don't think Sakurai liked that, so he took Brawl into a totally different direction, I can undestand why that pisses people off, but as far as I'm concerned that makes him my freaking hero, I'm glad tourney players are switching back to Melee because they would ruin Brawl just like they did that game. I said it once and I'll say it again. Melee is overrated as a competitive game, it was never meant to be a competitive game. Just about every other fighting game out there is superior in that department.
I find it odd that one of the most popular tourney fighters is a game that was designed to be the exact opposite of a tourney fighter.