I think Ann Coulter is hands down the most vile.
Coulter is far worse than the other pundits not just because of her distortions (which are par for the course for pundits), but her message. She's called for mass murder of civilians, massive use of internment camps against political dissidents, forced religious conversion, etc. I've seen her make ethnic/religious slurs against Arabs and claim that women shouldn't be allowed to vote. She even fully defends Joseph McCarthy's witch hunts down to the last detail and recommends similar actions today.
IMO the sheer cruelty and authoritarian nature of Coulter's views can't be matched by anyone else in the mainstream.