To contradict this generalization as it pertains to Shakespeare's Romeo and Juliet, it is Romeo who consents to attend the fete that the Capulets have and look. When he does see Juliet, it is Romeo who falls instantly in love. Therefore, Romeo is the one who chooses on looks. Juliet is hesitant to touch him when he offers her his hand as "a good pilgrim"; she is not the one swearing by the moon, either.
Earlier in the play, when Lady Capulet asks Juliet about Paris--"What say you? can you love the gentleman?"--Juliet replies,
I'll look to like, if looking liking move./But no more deep will I endart mine eye/Than your consent gives strength to make it fly. (I,iii,101-103)
It is again Romeo, rather than Juliet who is infatuated with appearances in Act II. For, after he scales the walls of the Capulet orchard, he stands in awe under her balcony:
But soft! What light through yonder window breaks?
It is the east, and Juliet is the sun!
Arise, fair sun, and kill the envious moon,
Who is already sick and pale with grief
That though her maid art far more fair than she....
See how she leans her cheek upon her hand!
Oh! that I were a glove upon that hand
That I might touch that cheek! II,ii,1-25)
First of all, you are assuming that women do actually choose on looks and not on how nice a person is. You have surely seen ugly men with wives or girlfriends, so you know that this is not always true.
Second, you can argue that human beings have evolved to prefer people who look good. We presumably want to have children with people who are "fit." If we do, then our genes can live on. This could make us naturally want to reproduce with people who look good because looking good might signal to us that they have good genes and are good survivors.
Some further clarification is needed. Initially, I think it might be a bit on the sweeping side to say that one gender choose others on the basis of looks. Undoubtedly, this is present, but to say that it is something that serves as the only determinant might be a bit narrow in scope. There are many reasons individuals are attracted to others. Looks might not play a role at times, economics might. Another determinant might be emotional compatibility, or even similar temperaments and tastes. Some might not even choose another at all, but rather the choice being made for them. There are multiple reasons why individuals choose to be with others. (The only time I can add a personal note: I am confident that my wife did not select me on looks. Recently, I had a student tell me, after seeing my wife, "Man, you married up!" I looked at the student that they were absolutely right! In this instance, a women did not choose on looks.)
I have to say that it is not just women who go for physical appearance. Men are also attracted physically. It has to do with the way animals work. Humans fall into this section when it comes to our mating habits.
In nature males flaunt their feather, make odd noises or budge up to look more attractive for the female. In return the strongest or best looking one wins. It is also about natural selection. The fittest is the one that one is normally drawn towards.
I once heard my friend who was a sociology professor say that he was glad that he had married young because he had nothing to show to get a woman once he had hit his fifties. Physical attraction is just what it is.
However, there are plenty of people out there and the great thing is that what features one person is attracted to are not always the same features another person is attracted to. Therefore, there are some fish in that sea that are going to find you attractive just as you are. Keep being nice.
By doing some searching of my own, and self-reflection to boot, most people must agree that this has been a time honored question. There are many sides to this argument, but it truly boils down to your own personality and preferences. Some people are raised within a culture that promotes physical beauty over intellect. It could have to do with the generation in which you were growing up. Hopefully the links I have provided will give several prospectives on the subject that is helpful to your question.