Depends if you're looking to play it at a casual level, or a competitive level. If you're looking to play at a competitive level, Melee is the superior game, due to its speed, and technical aspect. Smash 4 can also be competitive, with the characters being more balanced, and more accessable, though its's not really technical, and slower than Melee. Not saying that Smash 4 is a bad competitive competitive game, it's still really good, and fun to play at a competitive level.

For casual gameplay, they're all good, though the characters are really easy to unlock in Smash 4 compared to the other games. I still highly recommend buying Smash 4 if you haven't already.

Melee is the greatest game ever made so it has that going for it

PeoplesChamp