Least favorite - don't know enough of them so... can't really answer the question on that one. But I don't like people who swear, so it's always kind of unpleasant to watch Gordon Ramsey -even though he's brilliant at cooking and gives smart advice... I just don't like the swearing.
Hahahaha I agree that Rachel Ray is annoying as HELL, but damn is she a looker! Even that pic you posted is completely silly and cheesy (what is that look on her face?), but it still works for me. I'm just a sucker for a woman and some chocolate though, as many on people GaG have come to know. Haha!
Anyway, my favorite is probably Jamie Oliver. The work he did with school nutrition is incredibly admirable.
Honorable mention would be Rachel Ray, for reasons mentioned above.
My least favorite would be Paula Deen. Because racism.