Oh, how can you expect me to answer that? XD I love them both.
Both of them appeal to me in their own different way. Angel is a brooding, soppy mess of angst and dark charisma. I watch him when I'm in the mood to cry, because Boreanaz has a kicked puppy look that could make the most unforgiving Grinch's heart grow two sizes. And I'm a sap to start with. I can't tell you how many boxes of Kleenex I've gone through watching the Angel Angst Machine. I should've collected them, I could've built something out of them.
Spike on the other hand is a sarcastic bad boy with the heart of a poet and a lover, and charm oozing out of his ears. (I'm pretty sure that's the reason his hair's that color.) He'll suck the life out of you and make you think it was a fun party. Plus he's British. Where does that not get fun: a badass English vamp?
Both characters are equal parts cool, funny and angsty. And it bears mention: David Boreanaz and James Marsters are both hot. At what point did any of that become unappealing? XD