If we are talking about relationships, then I suppose there are different situations. You may be out in a bar/club and see someone and think "Oooh. They're a bit of allright". So looks are what first attracts you to them. You may chat to them and enjoy their personality, which can make the attraction stronger. However, they might be really boring, unfunny etc. This can lessen the initial attraction and change your feelings.
You can also meet someone who you don't find attractive at all, but once you get to know them, their personality can make the attraction grow.
I suppose it depends on what you are looking for. If it's for a one night stand then go for the looks.
No seriously. You cannot base a relationship on looks alone. If you do, it will never work out.