hello "kababayan!"
we dont know for sure, celebrities have to keep a sort of "role model" image you know, especially for someone like him playing the role of-- what can now be considered as-- an "icon" to be emulated by kids worldwide..
but let's not be so hard on Dan, he can prove himself in years to come, when he's out of the HP franchise.
But as of now, he's doing great! & we have to give him real credit for that. Remember he's growing up & I sincerely hope he doesnt change.
..and going back to topic!.. who else could be ugliest but ELOISE MIDGEN.. the poor girl.
The meanest in Harry Potter is ultimately Voldemort, since he's the one who took people's fear and prejudice and twisted it to his own devices.
However, since you don't see a lot of Voldemort, probably Umbridge and Snape would get top billing from most people.
(NOTE: My opinion has nothing to do with the characters. Alan Rickman is an extremely talented bloke and I don't even know who's playing Voldemort or Umbridge yet, so there is no prejudism here!)
And as for the ugliest (in JKRowling's descriptions anyway), I would like to nominate her frogginess Umbridge. The frog-face depictions of her just sound disgusting. BLECH!