re: Better physical comedian/actor in their prime- Michael Richards or Jim Carrey?

Peter Sellers
Steve Martin (and in case you think this is just Pink Panter related I have never seen any of the Steve Martin Pink Panther movies)

Chevy Chase

Bob Hoskins (don't laugh at this if you have not seen Who Framed Roger Rabbit? remember he had no one to play off of during the filming)

Tim Curry

Sid Caesar

Jonathan Winters

Leslie Nielson

I want to put Robin Williams on this list but I really can't think of a role he had that really showcased his abilities as well as his stand up material did unless you want to count Mork.