The voice, the brains, the looks (yes, I know I'm weird), and the kindness that sometimes shines through. And the sense of humour. Yes, he's got one, if you look closely ;)
I myself like men who can be dominant - others can't defend themselves against me and run away scared.

Zevran on the other hand - I like the character, but I could never find him attractive. He's got that Latin-Lover thing going on (not just the accent, the whole attitude) and that has always deeply repulsed me for some reason. But to each their own, I suppose. Couldn't bring myself to romance him with any of my Wardens yet...