Seth MacFarlane by far.
Consider this, years ago he helped write on and launch the original "Johnny Bravo" back in the day, that takeoff helped the careers of Butch Hartman, Genndy Tarkarvosky and Craig McCracken who forged the Fairly OddParents, Powerpuff Girls, Foster's Home for Imaginary Parents, and basically gave way to a lot of the kid shows we have right now. Seth also is great friends and feeds ideas with Matt Groening, despite everyone saying how he rips off "The Simpsons". His own show, Family Guy, has been immensely successful, launching four spin-off movies, three of which are based on a concept done and approved by George Lucas, two spin-off shows currently also on network television.
In terms of impact, Seth MacFarlane has his hands in a lot of different projects, shows and movies, which has aided in a lot of people's careers going forward. Chappelle has a few catchphrases and his show and stand-up sets are hilarious, there is no diminishing that at all, but aside from that what other impact has he had?? What careers has he furthered, what trends has he started that maintain to today, what has he done since Block Party?? Yes, he refused to fall in Hollywood's standards and that is respectable, but what else??
Chappelle is funnier (by the way, people need to watch Eddie Murphy Raw and stop disrespecting the man, give him his due), but MacFarlane has had a far greater impact for pop culture and continues to do so.