I haven't played the N64 title so it will not be included here.
5. Super Smash Bros. for Wii U
I'm not sure what it is with this game. Something just felt off whenever I played it. The lack of engaging single player modes is a turn off, graphically the game looks... OK, some characters are so blatantly overpowered. But that's not my problem with it. As a competitive/party game, those are things I can overlook (except the extremely unbalanced roster), but this game just feels weird to play. Maybe because I mostly played the 3DS version and didn't get a lot of experience with this one as a result.
4. Super Smash Bros. for 3DS
I preferred this one over the Wii U version for a few reasons: Smash Run is actually a somewhat decent mode, the 3DS graphics are charming, it's handheld, and the 3DS felt very good to me as a controller since I was used to it (leading to me using it as my primary controller for Wii U). It suffers from the same problems Wii U had, but it felt better to me as a whole.
3. Super Smash Bros. Brawl
This is probably the most nostalgic Smash game for me, as I spent countless hours playing it at home with my friends in school and running through the Subspace Emissary with one of my best friends. The slower pace felt a little weird after having played Melee, but I didn't hate it. The main problem with the game from a gameplay standpoint is the tripping, which was extremely annoying. Brawl had a great character roster, a fun and engaging story mode, and just provided so many hours of fun for me. One huge issue with it, however, was that the game came on a double-layered disc, which my Wii stopped being able to read after a while, so I was unable to continue playing. Also the graphics don't fit a lot of the characters at all.
2. Super Smash Bros. Melee
This game was so much fun for me as a kid. Brawl is a more nostalgic game for me overall, but I still have many fond memories of playing this with my family. Overall, the game has few problems, with a relatively balanced character roster, intense fast-paced gameplay, awesome single player modes and great event matches. Close to a perfect game, if I'm being honest. I really don't have anything to complain about.
But as great as Melee is, it's hard to beat...
1. Super Smash Bros. Ultimate
It's in the title. With every single character from the previous games and nearly every single stage, plus several new faces, it really is the ultimate Smash Bros. experience. World of Light was a really fun and surprisingly challenging game mode that I spent hours completing and never got bored of. The gameplay feels really good, probably the best in the series. Graphically, the game looks amazing, bar a few character textures that I'm not huge on. The massive collection of music includes some of the best pieces of music in Nintendo's library, plus some of the best tracks from other third party games. Overall, this is easily the best Smash Bros. game to date and I honestly don't know if they'll ever top it.