I agree with Barfly, depends on the girl. If you've already banged the girl, its nothing new, so a beej is much easier. But basically, everyone wants to get laid.
Sex. If a girl sucks at giving head and a lot of them do suck, then at least you can just pound her. There are also no women who I'd let suck me off that I wouldn't have sex with.. That's how I roll. If she's good enough to suck me off, then I'll hit it also.
I'm picky, but not too picky. For instance, I'll do the biggest, trashiest, whore you've ever met BUT they have to be somewhat decent looking to me. I have trouble trying to fuck a girl that I'm not in the least attracted to, believe me I've tried.
From the gals perspective, rather take sex over bjs anytime. Just don't like the freaking taste of it, to be honest and the smell doesn't help either (I know the same can be said about chicks too) but personal preference I'd rather pass on them.
I like both sex is better but thats probably because i'm with somebody I really love, but BJs are also really great and my gf is great at them. I guess it does depend on the girl, I've been with some girls who just didnt have a clue what she was doing down there.