All four are fantastic.
Personally, I think Bonham has influenced more drummers than Peart. Not to say he's better, but he's been more of a creative force that others have benchmarked off of. I might be short-sighted on this one, since I feel Bonham's presence in my playing more than Peart's. But I'll stand by what I say.
That said, Peart is more technically sound and proficient. He's the uber god amongst the gods you've listed. Drumming to drummers is a lot like bodybuilding in some ways. We all think Ronnie 2003 is a god, but he's not what makes most work out; the more achievable physique drives the day to day behaviors that lead to physique building.
Peart's proficiency is very much out of the reach of the average drummer - he's like 2003 Ronnie. Bonhman, on the other hand, is more aspirational. Zep's music is easier to relate to, Bonham's drumming is not as time-signature heavy and progressive, and though it is far from easy to master, trying to emulate Bonham after a few years leaves one with a feeling of satisfaction that you can at least hold your own; there's nothing satisfying about trying to sound like Peart and failing miserably. In bodybuilding terms, Peart is a 2003 Ronnie...probably will never be anything like him ever again, and try as you may, you won't even come close to him. Bonhman is like a late 60's Arnold. Not really within reach, but you hear him and think "I can do that". Just like a young dog sees a late 60s Arnold and thinks "I can do that". Even though, he probably can't, he can come somewhat close and feel better about himself doing it.
So for me, Bonham is way cooler. And more influential. But Peart is the best, just like Ronnie 2003 shits all over anything anyone else has ever done.
Keith Moon...I'm sorry. I don't get it. I keep listening to the Who looking for that feeling that's inspired so many drummers, and I don't get it. He's great, but I don't get it, personally. That said, I feel like an idiot by not voting him into the top 4 because I think I just don't get it, so that's my fault.
For what it's worth, if you were listing the best four drummers from the 60s/70s in modern rock, you would have listed Ginger Baker instead of Mitch Mitchell (who is awesome by the way, but not in Baker's league).
And that's my feeling on that.
