Considering the direction that Nolan has taken with the series, the Penguin is the worse idea (as Nolan, himself, stated). I don't mind the Riddler or even Depp. Depp is a great actor and I have enjoyed most things he has been in, but he's far too obvious a pick. If Nolan wants to hit another "homerun" like he did with Ledger, he might consider Daniel Day Lewis. Philip Seymour Hoffman is a great choice too, but not to play the Penguin. Maybe he can have all three actors in the film, but not necessarily in obvious roles.