Deadpool>Zeus imo, but the problem is, who's in all the best games involving Marvel? Wolverine. He's been in the old arcade X-Mens, the Genesis X-Men, the 3 MvC's, etc.
Wolverine doesn't sound very "Playstationy" in my opinion.
But he has absoultely no relevance to playstation history. This game is a crossover of playstation characters, characters that have had prominence on playstation consoles and helped defined playstation as a whole, Deadpool does not fit into this criteria whatsoever. And just because Raiden, Big Daddy and Isaac made it, is no reason for there to be another character with no playstation history at all to be added.
Deadpool has as much relationship with Playstation as Batman
My only condition for buying DLC characters is, they need a creative moveset and need to be originated from videogames. So no to Deadpool, Goku, Batman, Harry Potter, Naruto, ET, whatever.
[Bats and Dead would be pretty awesome though xD]