Melee
Melee took everything great about the original, made it faster, prettier, and more refined. My only major complaint was Wave Dashing because it made some characters incredibly unbalanced, and I personally believe using a game exploit should not be a requirement for competitive play.
Brawl had messed up physics, more character balancing issues, extremely repetitive single player modes, smaller stages (making Sonic not so useful), a nerfed Mario, completely unbalanced items, less responsive controls, and generally a slower gaming experience. Everywhere they made a step forward, they took a step back in already established parts of the game. They hyped the crap out of the game only to pull several dick moves.
Edit: I was also pissed they removed Mewtwo. He was the only non-clone they removed, and he was arguably the most unique fighter in Melee because he required a completely different strategy to use well. Giving us the butt-ugly trophy that was difficult to unlock was a kick in the nuts, too.