all depends, are you likely to make it to the end of the movie before you get distracted? If not then dont watch anything that requires too much concentration.

how far have you got with this girl? scary movies are good so long as youre man enough not to be hiding behind the sofa before she needs someone to hug up to.

has she asked as some kind of test of your taste/intelligence/whatever?

otherwise pick something light and funny (old school/anger management/...)

All depends on the girl fella!