Marvin Lewis isn't great, but he's not the worst either. I've been following football long enough to realize that a small market team has to be grateful for even the mediocre talent it gets.
However, if we do change coaches, I love the idea of Billick (if he's even interested in coaching again), Zimmer (He's earned a shot anyways) or a young guy like Harbaugh.
If you're asking me, I'd leave gruden out of this discussion. I don't really want to watch 4-5 QB's with promise sit on the bench while he tries to figure out which one is best.