Not so much nationality, but definitely by gender/race. My general reaction to black comedians is that all the jokes will be about how hard it is to be black and funny impressions of white people in business suits. It's not that racial comedy is bad, but Richard Pryor did it better 30 years ago than most people do it today. Obviously not all black comics are like that, and I like some, it's just my initial bias.

Same with female comedians. I'm not sure I could name one I really found especially funny. I do like Sarah Silverman's show, and her style is really out there and I think it can be pretty funny, but Jesus Is Magic wasn't that great, from what I watched of it.