Not bothering with third-parties, there aren't any I really want (there are some I wouldn't mind seeing, but none with realistic chances and honestly I don't necessarily feel like they should be in Smash).
Top 5 (Nintendo) DLC Characters:
King K. Rool
Isaac
Lip
Dixie Kong
Sami
Don't care about Inklings. Expect them in next Smash, but not as DLC for this one.
K. Rool is obvious, main DKC baddy, hilarious mannerisms and personality, excellent potential.
Isaac I will agree doesn't have much of a personality. But he's the main character you think of from the Golden Sun franchise; the original main protagonist. He's got all the moveset potential in the world, far more than any other character, and Golden Sun is such an amazing franchise it simply deserves to get in.
Lip because I love Panel de Pon. I know she's unrealistic and obscure but I don't care, I love Panel de Pon and want it to get more attention.
Dixie Kong is also obvious.
Sami because Advance Wars. I think Sami is a lot more interesting than Andy and she's just as important as he is (granted, so is Max), and I simply think Sami is a much better character.
EDIT:
The only third-party I'd like to see get in is Bomberman. The only third-party I can see getting in is... well, that's really hard. I think Snake is unrealistic at this point, and since Ubisoft is also asking people to vote for Rayman, I'd say that Nintendo probably denied Rayman getting into Smash as well (this has been a rumor popping up), so a second denial is just as likely as the first for both Rayman and Snake.
Maybe Professor Layton I guess. He's not a big well-known name, but the franchise has been Nintendo exclusive for a LONG time.