Actually, I think that the fact that their styles were so different makes it that much easier to compare them...or rather, "contrast" them, which is what really needs to be done.
As for comparing them, I think that Bonham
could do anything Moon did. I don't think Moon had any skills that Bonham didn't have. I'm not sure about the other way around. I say I'm not sure because Moon rarely played with any control so it's hard to judge him conventionally.
I think Moon created alot more anarchy and chaos into the Who's live show, which worked well for the Who onstage, and pretty much played with reckless abandon most of the time.
I think Bonham added power and energy and excitement to Led Zeppelin and could do it while creating a great groove and feel...something that Moon didn't really ever bother trying.
Another oversimplification - Moon was more icing than cake, Bonham was more cake than icing.
As for who the drum "king" would be, I didn't want to hijack the thread for one thing, and my personal list of contenders would be pretty long and I don't feel like mentally sifting through it all right now.
Sounds like a good idea for a thread though