Polar extremes for the lose.
By "be with," do you mean enter a mutual exclusive more-than-friendly relationship, or just hang out?
If it is the former, then it depends how annoying the pretty person is. If they are not annoying in their stupidity, I'd choose that one (and tell them to STFU), else I'd choose celibacy. And if I still had to choose one, I'd choose murder. There is a certain minimum prerequisite of both physical attractiveness and intelligence&personality (neither of which are low) for me in that respect, if it is to be a more-than-friendly relationship.
If it is the latter though, then I'd choose the latter person. Interesting > Pretty in thast respect.
Bazz wrote:Not that I'm saying I dislike intellegence in a woman, far from it, but an explaination of some scientific concept is rarely cute no matter who says it.
[spoiler=:ono]Unless it is from Entr0pi3, clearly

[/spoiler]
Besides, intelligent people are often[*] clever enough to know when a scientific explanation of something is not appropriate. For me social skillz is part and parcel of intelligence, regardless of academic grades and shit.
[*] But not always for sure. Especially academics, many of whom seem to lack social skills on a practically autistic scale.