Best thing by far is if you can go together to pick out a couple of videos. That way she can’t complain if she doesn’t like them (well … actually she can, and she will if she feels that you are dragooning her into watching them). Anyway, select your shop carefully – preferably one that seems to be couple-friendly and has a minimum of sleazy-looking people hanging around.
Failing that, you’ll have to use your judgement – and ask her what she would like. In my experience women who watch porn usually enjoy couples sex; gang bangs are out and if there is group sex it should be relatively restrained. Action shots that emphasize the overall movements of the bodies rather than the actual mechanics of penis-in-vagina sex seem to be the go, too. Obviously anything in which the women appear to be being coerced into sex or to be in pain is not a good idea. A story line doesn't seem to be particularly important., though. Some women (including straight women) enjoy looking at girl-on-girl sex, others don’t seem to.
But these are all generalizations – best bet is to ask your girl and to use your knowledge of what she likes.
The Private series are often good for couples – are they available where you are?