I have one suggestion of a particular question you can ask them, which, in my considerable experience, will tell you EVERYTHING you need to know to make an informed choice.

Approach this question carefully so they don't panic, but all you need to do is to ask each of them to describe their relationship with their father. I know it sounds strange, but I wouldn't lead you astray. If you're dealing with women in their 20's, you can almost guarantee that a messed-up answer to that particular question will lead to a messed-up situation between you and the gal.