I don't think one can over rate George Carlin. Of all professions, a comedian - comedian! set policy for all broadcast media as to the words you can't say over the air. Now that's influential.
Those with a clean act, like Kathleen Madigan, really impress me. When I first heard Ron White's routine about how he got to the venue in a small plane, I was laughing so hard that I had a hard time breathing (it was live).
I think Rodney Dangerfield has the best joke I've ever heard....."My dad's an alcoholic....you mention work and he gets drunk." Clean, quick, a little bit of edge, somewhat self deprecating, widely understood and funny.
Overated are the late night hacks. Kimmel, Colbert, Maher, sadly, Jon Stewart lately, but the top prize goes to Fallon.
Underated? Me! Getting material ready to kill them at Thanksgiving dinner! Captive audience.
I miss Norm McDonald
Overrated = Jerry Seinfeld. Despite Seinfeld being one of the best shows of all-time. Plus the real genius behind the Seinfeld show was really Larry David anyway.
I was listening to Eddie Murphy Delirious a couple of months ago, still hilarious 40 years later.
It's a shame Bill Cosby turned out to be sexual predator. His routines were always clean. I would play his albums on long car trips when my kids were young and they would laugh like crazy and the time would go by fast.
One I think is underrated is Greg Warren
Overrated; Jim Gaffigan. IMO I don't think he's that funny and his voice is whiney.