Stephen Colbert or Sacha Baron Cohen (Ali G)?
It's a close call. Colbert recently did the White House Correspondent's Dinner, "(attended by the President, the elite of Washington politics, and the White House Press Corps) and told the truth. Jaws dropped. Eyes popped. The live audience gasped. Scalia laughed his ass off. You want to see a brilliant comic display some real courage? Look no further. Enjoy the reaction shots, and Colbert's audition for Press Secretary job." (quote from Slashdot). I'm not sure who in the West Wing decided to hire Mr. Colbert, but I'm sure they've been spending a lot of time on Monster.com recently. Among other things, Colbert joked about the Plame Affair, Cheney's Birdshot, Iraq, Fox News, Bush's approval rating... My favorite line? "Reality has a well-known liberal bias." :-D So, a gutsy man for a tough crowd.
As an aside, that's one of the problems when a Republican president is elected - Republican comics are few and far between. Both Ben Stein and Drew Carey have done the Correspondent's Dinner under Bush, and I watched Stein - he bombed so badly that the Pentagon immediately bought him for $2.6 billion. It's kind of like the Academy Awards (going to the opposite end of the political spectrum, but staying elitist). Jon Stewart bombed because Hollywood types can't take a joke that's not approved by their publicist. But I digress.
Ali G takes risks far more often, and with people who are much less restrained when it comes to physical retaliation. I.e. he and his crew have been both assaulted and arrested in the line of duty. Mainly when he plays Bruno - his flamboyantly gay Austrian character - schmoozing with the folks at, say, a gun show in Atlanta. Or Borat, the Kazakhstani who is clueless that Americans may find some of this customs to be a bit awkward. And finally, Ali G, "the only interviewer prepared to ask the really difficult questions like "what was it like to walk on the sun?" to Buzz Aldrin or asking the ex head of the FBI to cast his mind back to the grassy knoll and ask "who really shot JR?" (from Official Site).
So who's more gutsy? All I know is, Colbert probably shouldn't say anything private on his home telephone anymore.