pure gameplay:
melee > ultimate > 64 > brawl > WiiU/3DS
but the roster makes meele and ultimate both on 1st place for me and 64 at the end.
Also imo more interesting characters were released with later games.
Tho more stupid characters, that are not fun to play against too...
Imo in 64 as a casual player speaking, all characters were fun to play against.