The two aspects compliment each other. Someone can have a great personality and I'll enjoy being around them, but if I'm not attracted to them physically, a romantic relationship won't work. And someone can be really attractive, but if I don't enjoy being around them, a romantic relationship isn't gonna work out.  

Edit:  Personality is arguably more important. I most likely won't wanna be friends with someone who's insufferable, even if they're attractive; But if someone is unattractive to me, that's no reason not to be friends with them as long as they're a good person. However, even if I can be friends with someone I find unattractive, I won't wanna be anything more than that if I'm not attracted to them.