Conan.. never funny ... F-
Stanhope, Cross, Black, Louis...haven't heard of them.
Pryor... I give him a C+ at best.
Carlin and Hedberg... A+
Not going to quibble over Conan. I haven't watched him since I was undergrad at LSU and everyone watched him. I remember enjoying it, but it could very well have been F material.
I love Pryor. I listened to him with my Dad long before I should have and way earlier than I would've understood most of what he said.
If you like Carlin, you might dig Stanhope. Carlin is in a league of his own, but you can see the influence on Stanhope's standup.
David Cross is a bit more hit and miss than the others on the list, imo. But when he hits, it's pretty good.
Lewis Black is consistently funny for me.
Louis CK is another one that's pretty consistently enjoyable.
I tried ranking them... but couldn't. Hedberg and Carlin would top it, for sure. Not certain about the rest, though.