First of all - they really hate Louis C.K. although I know some people like him - I have heard worse.
I don't even consider Bill Mahr a comedian anymore - he is a commentator.
I like Woody Allen, but as a standup, at #4, I dont think so.
I never liked Johnathon Winters that much.
I actually think Joan Rivers was hilarious in her day - her original act was killer funny. Far better than Ellen Degeneris.
Jerry Seinfeld's show was funny - but as a standup, dry cleaner jokes, really?
Eddy Izzard had one HBO show that was hilarious, but a second one really flopped.
I would personally put Robin Williams higher, but I know some people don't like him.