Good idea Smeags!

64: Never played (shame on me)

Melee: Peach (I only played Melee with my brothers and had no knowing of the tournament scene so I didn't know Peach was actually top tier. I just loved hitting people a frying pan, a golf club or a tennis racquet and how incredible her down smash was.)

Brawl: Peach (Although she got a lot of nerfs I still stuck by Peach while playing Brawl. People weren't used to fighting against her and you could surprise an opponent with all her trick and tactics.)
I played Brawl a lot more than Melee so I also had others "mains", namely Pikachu (drove people crazy!) and Diddy Kong (banana madness!)

There is a picture on GAF somewhere showing Mario's alternate attacks.  Normal cape can become a gust cape or a spark cape for example.  FLUDD and its pressure output gets altered.  Fireball we have seen.

I only played Brawl and that was non-competitively.  I mostly played Pit he is looking substantially improved, also liked using both Links and Lucario.  Expecting to drop both Links for new comers.  Greninja looks locked down as a yes for me.

64: Yoshi
Melee: Peach
Brawl: Peach/Toon Link

64 - Ness
GCN - Link/Samus
Brawl - Random (seriously, I liked playing as lucario most, but I almost always chose randomly)

N64: Link

GC: Link

Wii: Ike!!!!!!!!!!!!!!!

"Is this a match made in heaven? Remember, no matter how big you may be, there is always someone bigger."

N64:Luigi
SSBM:Luigi/Roy
SSBB:Olimar
SSBU:Olimar/Villager

N64 - Jigglypuff and Samus...
Melee - Jigglypuff...
Brawl - R.O.B., Olimar, and Peach...

N64- Samus and Ness
GC- Samus and Mario
Brawl- Ness

"Here's Link in an outfit based on his ordinary clothes in Skyward Sword! The art style looks a little different, but the actual clothing model is still his usual tunic."