I would say smash 1 and 4(3ds). Even though smash 1 was the one that brought this magnificent beauty into our lives, it's rarely ever mentioned and no one talks about it. And the 3ds version is just as irrelevant. At least the Wii U version is talked about now(it'll disappear as well in the future). I don't think people will ever stop talking about melee, brawl or ultimate. Funny the ones with actual names are the most relevant, at least to me.
Just a guy who doesn't want to be bored. Also