Could someone give me some dating advice?

There is a girl who i just met and really like, she is pretty and nice and we email/chat a lot and are going to go on a sort of date but not really. I asked her to my school fair (she goes to a different school) I also really like her. There is another girl who basically asked me to ask her out, and i did. We have been off and on again for about three times, and this would be the fifth. We are going to go on a date this saturday. I like her also. Which one should i chose?