If there was going to be a new character in SSBB, and I had to choose, I would make it Dark Samus. She is so kickass. Tons of phazon based attacks and the ability to become entirely phazon saturated as an Ultra-Smash. Since she is the arch-enemy of Samus in every Prime game (in MP1 as Metroid Prime)...
If not, I want Ridley (either SNES Ridley, or Meta Ridley). I want to be able to crush my oponents under my heel with the might of the fire breathing space pirate leader. I want to fly for brief periods of time (like Meta Knight almost), attack opponents with spinning wing+tail combos, crush opponents within my jaws, and perform vicious claw and teeth attacks, lunges, etc... If its Meta Ridley, I think the orange energy wings should be deactive (as they are after you destroy them in MP1), and turn on every time he flaps them or attacks with them. He also should have some cool weapons to use on you like Meson Bombs (used like Samus's bombs) and Cluster Missile barrages. His Ultra-Smash might make him immortal. So basically, if you kill him he comes back to life without you getting the kill. Since.. It doesn't matter how many time you kill Ridley. He will appear in every Metroid Game to kill you. I swear, Ridley has more lifes than a...Kane. You thought I was gunna say Cat.