I think what attracts most people to each other is what you see first, so I would say looks. What keeps you interested with that person would be their personality. Everyone is different like for me I'd rather have personality first. Someone with the best looks can turn out to be the ugliest person on the inside. So decide which is more important to you!
That would depend on the girl you are asking. Shallow, fake girls want looks. Down to earth, girls with brains want a personality. ... And if it's not too much to ask for, someone who is not an eyesore. :)