It's funny when you ask this question to someone. They generally give you the answer that you want to hear, but not what they really think. I've heard that personality is king, but then the same people that say that, always chase after the runway model; in all fairness, it happens moreso with the males than the females, but it still happens.
I suppose the real answer lies in where you stand in the "relationship" time wise. If it's at the start of the relationship, then it's definitely going to be looks, no doubt about it. People will lie through their teeth to say otherwise, but we all know that looks really do count in the beginning. How often does the single geekish male / female, get picked over the chiseled jaw jock / model in the making feminine?
But after time, the familiarity of the look, will start to bore you, and it's the substance, rather than the style that counts. This is where the personality kicks in, in relation to importance in a relationship. You can only look, and admire something for so long, when you're trying to have an educated / fun conversation; if there's no personality, might as well talk to a rose; just as elegant and beautiful, and you'll probably get the same conversation out of it too... =D
Though some people will grin and bear it, for the sake of having one, rather than none.