When it comes to these comedians, Louis C.K., Conan O'Brian, and Jon Stewart, certainly have their heads on straight. Bill Maher is extremely LEFT, but doesn't keep it concealed like Jon Stewart does. However Bill Maher is open minded and will gladly listen to what you have to say and let you tell your side... whether he agrees with you or not, he will respect your right to have that opinion.
As for George Carlin and Bill Hicks. George Carlin was a comedic genius, but his political humor although funny, wasn't entirely spot on and a bit biased. Unlike Robin Williams who is a smart man, but whose political humor is not only spot on, but out of nowhere, but it came from somewhere.
I watched Bill Hicks last night and, yeah his conspiracy theory bullshit I don't care for. Imagine if he lived to 9/11/2001, what he would be saying in his stand-up. I do find his and George Carlin's religious material quite funny though. However we're looking at political humor here to judge a comedian... instead of their full comedy.