Draco Malfoy? Well...you said it's you're favourite character so I won't be too bad in my description...
He's arrogant, spoiled and makes me wish to transfigure him in a ferret every time he says or does something bad to Harry, Ron, Hermione or the other students. He really gets on my nerves!
But...but...I must admit that he's essential to the story, he's a part of Harry Potter books and I can't think of any story without him in it too.
And I think he's not that bad...he won't become an angel but I hope that when he'll really have to decide if he wants to support Voldemort or join Dumbledore in his battle against the dark lord he will think with his own mind and not just follow his father like he has done so far.
What about...er...Percy Weasley?