Pokemon is already adequately represented.
The Smash staple:
There are no other Smash-worthy Pokemon. It's already at 6 characters, one less than Mario which has 7.
There's enough Pokemon in smash. Mewtwo wasn't even needed but meleefags and nostalgiafags kept bitching.
I want new characters. Either from Nintendo or not. There's plenty to use. But at the same time I'd rather not get Smash overrun with too many shit characters.
I think it has enough Pokemon.
If I absolutely had to choose however, I would choose Gardevoir, and that's not just because of the fact it's my favorite Pokemon; it's in Pokken and it's popular. Some of the fans tried to make a moveset for it and there where some surprisingly cool/creative things, too.
/thread. Most patrician taste ever right here.
I'd choose Snorlax, Primeape, or Hitmontop.
Snorlax because he is my favorite and I'd love to use Body Slam on some mother fuckers.
Primeape because he would just be a fun guy to play as.
Hitmontop because he is pretty much a perfect fighting type.