Tuon for being sheer evil - Mat isn't my favourite character by any stretch, but I think he deserved better than her! I was really hoping something terrible was going to happen to the whole Seanchan race and the damane and 'property' could go free.
Faile - again Perrin deserved much better. But...
Tuon. As an individual character, my least favourite would have to be her, but I hated the whole Seanchan nation, and kept hoping something truly terrible would happen to the lot of them (except the damane and those held as 'property'). I was really sorry when it didn't.
Mind you, considering...