I always loved pissed off, self deprecating comedians who were personal and irreverent.
I have to go with Eminem.
The greatest comedians go after everyone (every group) and everything then they attack themselves.
Carlin, Pryor, Hicks, Kinnison...so forth.
Ballot(s) would go towards Patton Oswalt, Chris Rock, Chapelle, C.K., Patrice, Giraldo, and especially Bill Burr.
Hell, even the late great Bernie Mac said Eminem when asked that very question.
It takes time to write bits and have it flow onstage.
Most rappers take themselves too seriously. And couldn't handle a heckler besides calling security.
Have you guys seen that Fresh Prince episode where Will thought he could be a comedian, fail, and then have his boy D.L. Hughly bail him out while Will was eating his balls?
Most rappers.
A clever line or story can be a laugh but try doing that shyt for 15 mins. to an hour.