Luckily, i've got both, Carlos is both smart and hot looking ;-)..
..
But if I had to pick I'd go with smarter, for me, it all starts and ends in the mind ......

Frankly, there's a unique charm to less-attractive and dumber people which is so often overlooked. They are so grateful for one's attentions and affections, with the bonus of making one look freakin' brilliant and undeniably gorgeous in comparison. So I say, let's hear it for the dumb-ass butt-uglies!..

I've been with both, and they are both tough positions to be in. Ideally I'd go for someone who was roughly as attractive as me, and roughly as intelligent. When the other person is smarter, it's hard for me b/c i always feel I have to prove myself and carry my own weight intellectually. Not that I'm dumb, but the constant feeling of being not as-smart-as is hard for me to live with. And of course being with someone more attractive can be difficult because of the insecurities that crop up - will they leave me for someone better looking? what do they see in me? what do other people think about why we're together? etc. But if i had to choose, I'd say someone more attractive, but not a totally stupid person either. They have to be able to understand my sense of humor and talk intelligently about different subjects. Otherwise it just doesn't work for me (for more than a night at least! ;-)) ...

Probably smarter, that's more valuable in the long run...

I'd go with smarter because the smarter someone is, the better looking they become. The opposite affect happens with someone who looks great initially, then they open their mouth and dumbness falls out. The looks just seem to evaporate right there...
..
My sweetie is both smart and beautiful. But I fell for his wit and intelligence before I even met him in person. So his good looks were the icing on the cake...