You need to have the right balance of looks and personality. Its no good for a girl to be hella nice, but to look as if she was beaten by an ugly stick. But its no better to have a gorgeous girl who's as smart as your average chimp.
In my case, I tend to go with girls who have better personalities than looks. (like 60-65% personality, 35-40% looks).
I can relate to your situation because it happened to me (kinda). Im dating my best friend, she's great, she might not be the prettiest (she is v. beautiful nonetheless), but with her combination of looks and personality, she is perfect for me.
And im so happy to be with her, because we are much more than just a couple, we are best friends, and I feel that that adds something very specail to the relationship.