Which girl to pursue?

Doesn't sound like either of them are your ideal girlfriend. You may want to ask the first girl why she's being catty all of a sudden. As for the second, flirting while she's single may not necessarily mean she will continue to do so while she's in a relationship. Maybe you should look for someone new, though, because starting something with either one of these girls sounds like it'll lead to some major drama, especially in a small school.