They are all equally bad

Ok, I've only played 2, but both bad

Hard hard choice. I've got a lot of nostalgia for the first three, all for various reasons, but if I'm choosing the best I think it has to be Ultimate. Melee is a close second, though.
I'll predict that the last Smash character is (and should be) the Doom Slayer. The man is a classic staple of gaming, represents a company not yet represented, has appeared on a Nintendo platform multiple times, and could have a robust and unique moveset.
In my deepest heart I wish it would be Phoenix Wright or Professor Layton, but I'm aware how unlikely either of them are.

Ultimate is the best fighting game I've ever played, a masterpiece.

I have no idea who the last fighter will be. I have the feeling I will be surprised either way.

Lol, why?

You really hate a lot of games it seems.

Hate is very strong word. I like the majority of games I play, I guess 

I never liked the gameplay, they are way too simplistic, playing with every character is almost the same and after few matches I always felt like I have nothing more to explore in mechanics 

On surface Smash really lack depth, the selling point seems to be the fact it portrays characters from other franchises which is like... a bad point for me? I like games with proper visual identity and character design, that's something a game like Smash will always fail to deliver no matter how fancy are the graphics and animations 

Melee and Brawl was the golden age for me. I haven't really liked a smash game since.

They are indeed all equally bad.
Im gonna go with the original SSB64 just because its the one I've played the most.

I played a lot of SSB64 in my teens, but Brawl is by far my favorite.

I always skipped a game so I haven’t played them all. I have and played the 64 game, Brawl and Ultimate, of which I didn’t play Brawl much though. I’d say Ultimate is easily the best one.

Bonus: Not sure, haven’t been keeping up with the last couple of additions so I don’t know who’s in by now. Above Doom Guy is mentioned, and I guess I’ll second that.

1. Ultimate
2. Wii U
3. Brawl
4. Melee
5. 3DS
6. Original