Molag Bal, whose sphere is the subjugation of others for its own sake, stands for everything I oppose, and gets my vote.
Mehrunes Dagon is unpleasant to be sure, but he is crude and petty and I do not find his sphere of Destruction as deeply sickening as Molag's. I will concede, however, that Dagon was the driving force behind many more large-scale disasters than Molag.
Sheogorath cannot be considered evil. I know you said to skip the whole 'daedra can't be evil' bit, but the Madgod must be chaotic, and therefore inconsistent in his morality.
I do not know enough of Namira to pass judgement.
Mephala the Webspinner is considered by the Dunmer to be one of the Good Daedra. While her methods are of dubious morality, and her motives unclear, she is not a significant threat, or truly evil.
Vaermina, whose sphere is dreams and nightmares. Dreams are a vital part of the mortal mind; nightmares a training ground where one prepares for future problems. Vaermina is not evil.
Boethiah is another one of the Good Daedra according to the Tribunal faith. She is definitely harsh and cruel, but evil? nah, don't think so.
Clavicus Vile is a confidence trickster, plain and simple. I wouldn't go so far as to call that evil.
Sangune's sphere is the indulgence of pleasure, something only harmful in excess. As Daedra go, he's little more than a nuisance.
Hircine's sphere of sport for the sake of adrenaline is questionable, but not truly evil.
Again, I cannot judge Meridia for lack of knowledge, but she annoys me.
Ditto for Peryite.
Malacath is a downtrodden outcast, and perhaps the least evil of all the Princes.
Nocturnal is yet another I know too little of. Her patronage of the Thieves' Guild doesn't speak too well of her, of course.
Azura is a [censored]. She's petty, manipulative, and selfish. She acts nice, but is nearly as evil as Dagon (just in a different way).
The Wretched Abyss. You're the only person I've seen actually call Herma-Mora by that name. He is the hardest for me to judge in terms of morality, because I, like him, believe knowledge to be power and ignorance to be crippling weakness. However, his methods of obtaining knowledge can border on obscene. Intellectual betterment is an admirable goal, worth going to great lengths to achieve, but at what point are the means no longer justified?