After playing Brawl and Melee, I have to honestly say that I enjoyed Melee better
Mostly because my biggest gripe is with the equalization in character movement. The fastest characters are barely better than the slowest ones.
Maybe it's because Melee had a bigger WOW facter involved.
My advice, if you are looking for a cheap game, get melee. If you want upgrades and online then get Brawl...