For me it's (and this is probably not the right phrase at all), smart humour. I love sharpness and people who have words a will. Some great comedians have a knack of being able to talk to audience members and towards the end of the show bring it right back to that same audience member, it's just brilliant. I don't get slapstick humor, although I do realize it can be well thought out, I personally just don't find it funny, although it reduces my 3 year old to belly laughs!
It's really just a matter of taste, we all find different things funny, I just happen to like wit and in a lot of instances alternative comedy!