Melee.
I will say it right now, going and playing Smash 4 right after playing a session of Melee is painful. You have so much more control over your fighter's movement in Melee, and it is so unequivocally satisfying to chain together attacks and drive your opponent across the stage, no matter how many times you do it. You have all this freedom, and then you play Smash 4, and it feels so... rigid in comparison.
And it's not just game physics either. Melee has all the content it needs. It has all the characters, stages, trophies, and game modes so that it can keep you satisfied and entertained without ever feeling like a cluttered cluster**** of... stuff, like what Smash 4 feels like to me sometimes. Not to mention, its music, sound effects, and graphics are all top quality.
So yeah, Melee is pretty swag.