They are both alright, I still play them but more casually these days, it's not like I drill wavedashes and shit anymore. I prefer Project M to either, I like having the Melee pace with more characters. Tr4sh is pretty fun when you get a crowd and max out the player slots, but 1on1 is just painful for me to watch and play.
Lots of people seem to really like 4, it always gets more entrants, though maybe that's because its easier to get into than Melee, both in getting the game and actually playing it. Pretty much everyone I know still plays it. Melee, on the other hand, has a smaller crowd playing it competitively, but they tend to also play 4. Still a lot of people, at one of the bigger locals all three games (PM, Melee, Tr4sh) get top billing over stuff like FIFA, COD, LoL and Rocket League. And the other is a Smash only event. As for 64, the little I have played it wasn't as fun as the rest. Melee and above really is a straight upgrade.
And yeah, once you move out of school/anime con-tier tournaments into something more organized you run into some beasts.