Hmm... The characters that I would really like to have in SSB are: King K. Rool, Dixie Kong, Ridley, Krystal, Tingle, Skull Kid and Toad.
If all or almost all of them are in the next SSB, I'd be so happy. I hope they put at least 15 new characters in the next game. It would be awesome. :)
I think Skull Kid would be a great character. He could blow things with his flute like in OOT or he could put on the Majora's Mask. :)
Another one would be Tingle, he has his own games, he appeared in some Zelda, so he is a principal character as well. He would also have great moves, like his...