I'm going to assume that the fictional lass in question has either a stellar or at least tolerably average personality. Otherwise answering this question makes me seem a little shallow or misogynistic, and those are both things I try to avoid, even hypothetically. So with that disclaimer aside:

My gut instinct upon reading your question was to say "body." Okay, actually my gut instinct was to go have sex with my wife, or eat lunch (my gut is very immature).

The body is the part you give sex at most of the time, and there's just plain more of it than there is of the face. Seems like to get the most bang for your buck--we are purchasing this woman, right?--body is where you want to invest your capital.

BUT, after giving it a lot of thought (and after silencing my gut with a burrito and a quickie, in that order), I'm actually going to go for the lady with the gorgeous face. My reasons:

Firstly, the face is the part of her I'm probably going to be interacting with and looking at most of the time. Even if it's resting atop a national disaster area, that's easier to ignore than a troll woman coming in for a kiss.

Secondly, I hear there are still sexy things you can do with a face. I mean, researchers are looking into it, and I'm nothing if not a scientific optimist. Go for it, face-sex researchers!

And finally, a girlfriend with a beautiful face and terrible body is easier to hide (hey, while we're being shallow). I note that you just said her body is NOT "drop dead gorgeous." As long as that doesn't imply hugely overweight, chances are whatever acne situation, lopsided bosom or prison tattoo is weirding me out can be covered with loose clothing, and I love me a woman in a muumuu and parachute pants.

On the other hand, it's pretty tough to hide an unflattering mug. I mean, it's not like I can make my wife wear a bag over her head all the time. Well, not in this country, anyway.

So there you go. The eyes have it (also the nose, mouth, and other parts of the face). I think you've actually stumbled upon a very interesting psychological test here. People who pick body are more concerned with what they're getting at home, whereas us face people are more concerned with how she reflects on us publicly.

I feel dirty for some reason. Hey, let me ask you one back: If you had to pick one, would you rather go for a dude with a perfect body, or s great sense of humor? Remember, you can't pick both, because that's cheating and there's only one of me and I'm married.