Olbermann pisses me off because of his asinine, elitist bullshit. Not to mention his horrible "comedy" style, which relies on rather dry, generic sarcasm. It's sort of like the same bullshit Jon Stewart and others have been regurgitating over the last 7 years.
O'Reilly strikes me as an old pimp unwillingly stuck in a new, expanding world he can't deal with sometimes. He's definintely not afraid to say stupid things, and I love his unwillingness to cater to politically correct-ness.