For favorite I'm going with Alton Brown just because he breaks things down into the science of cooking which is fascinating. For least favorite, I'd say Emeril Lagasse only because the show is a bit strange with a live band.
For least favorite I nominate Paula Dean. Had the occasion to meet her in 2006 at the Housewares Show in Chicago. Her phoney southern accent gets stale after awhile. How many times does one have to say 'Ya'll' in the same sentence. She didn't do or say anything about cooking but talked for 1/2 hour about her new husband. She's the only one I turn off on the Food Channel. Also if you watch her, she never gives out any recipe info as to amounts or times etc.
HMMM I like them all, My favorite would have to be Sandra Lee just because, I like the semi-homemade approach. I also like Alton Brown, he makes down to earth food that the every day joe can make.