Smash Games are awesome. This blog will tell you my favourite, what I like about, etc.
For the real answer, Wii U is my favourite, followed by Brawl, 3DS, Melee, and then N64. I have never played Project M. before though...
SSB Wii U: My favourite Smash game, this game is a lot of fun, played a tremendous amount of it, over 2000 matches, etc. The character selection is the same as the Nintendo 3DS Version and IS the best in the series, and the 4 of Us Network play Online after school, work, etc. I did think there were a few flaws, such as the game didn't feature the music I loved in Brawl and Melee. The graphics look amazing, and the Stage Builder is better and more improved. The stages are really cool, and Mario Galaxy is probably my favourite because the designs are outstanding and the music in the My Music is great. Speaking of that stage Super Mario Galaxy 2 is my favourite game of All-Time. The Amiibo and Character Customizations were pretty great. Okay, I will stop here.
Brawl: My second favourite in the series (and was my favourite before SSBU released), this game features a lot of cool stuff. Things such as the Stage Builder and My Music were introduced. The game brings decent, some awesome newcomers such as: Wolf, Meta Knight, Zero Suit Samus, Pit, etc. The stages are very awesome, the graphics look amazing for the Wii, and the controls are perfect but I mess up at times. The Melee Stages I enjoy a lot, and the music are awesome.
SSB 3DS: Not as good as the other two mentioned above, the 3DS Version is awesome as well. The character selection is the same as Wii U and is the best in the series. The graphics are amazing and the stages, music, etc. are outstanding. This is probably my second favourite handheld game of all time (first being Super Mario 3D Land) and the controls are perfect, so perfect I beat the living crap out of Level 9's these days. Fun Fact: I almost beat Classic 9.0 with Mario but I died at Master Core.
Melee: I think it is an okay game. The graphics are good for the Gamecube, and the character selection is great. I haven't played this game in AGES, and I don't even know where my copy of the game is... The controls are okay. The Music is awesome. The adventure mode is fun. I think it is a good game and you should try it out sometime.
64: I recently got back into this game recently. The game that started the SSB Series, the game is literally about "Nintendo All-Stars Fighting Each Other" I think it is a brilliant idea. The character selection is okay, features Mario, Luigi, DK, Pikachu, Link, etc. The stages are awesome, Hyrule Castle and Saffron City are my favourites. Peach's Castle is awesome along with Dream Land, etc. The graphics are great for the N64. I recommend you play this game because it is awesome.
Well guys and gals, there you have it! My favourite Smash Game, my opinions on all 5 pf the main ones, etc. Comment down of you want me to do a Top 10 List as a blog. ;)