When It Rains, It Pours...It Pours Conflict.

I have this problem. I talk to the girl from the Apprentice after party a lot (see, "To Make A Long Story Short), and yet, I still talk to that first girl fairly often too (see, "Insert Witty Comment by Roger Lodge Here"). Obviously, they don't know anything about each other. I'm still trying to gauge New Girl's interest, and to be honest, I'd love to let First Girl go. But I'm having a hard time doing that.
When I'm around First Girl, I'm indifferent. I'd rather she wasn't there, and I tend to look around a lot. I'm just kinda a dick when we're together. But, when we talk on the phone, and I don't have to worry about dodging her advances for public affection, things are great. She's smart, and actually kinda funny, in a cute way. Which can only mean one thing...we really should just be friends. Buuuut, how, in this day and age, where "let's just be friends" is so cringe-inducing, do you tell someone, "I swear I like you, I just don't like you. Let's be friends." Especially when one person wants to be more than friends. It's like my own little episode of The O.C.!
Anyway, I'm still feeling New Girl out. I'm a lot more attracted to her than First Girl, but I can't base my decision on that...or can I? Nah, I can't do that....right? I mean, I know for a fact neither of these girls is my soulmate. If one of them was, I wouldn't really be pondering any of this. Aside from that, she's a pretty cool chick. I like talking to her, even though she says a lot more in the conversations than I do. You know, one of those "gift of gab" people. I never understood that expression. Is it really a gift? The "gift of producing 'would you please shut the fuck up' looks in other people" would make more sense. Anyway, she's cool enough, which is all you really need in a girlfriend, because seriously, girl's who are awesome and superhot are very few and far between. And probably don't like you, anyway.
So I'm conflicted. How do I break things off with First Girl, without hurting her feelings, thus enabling us to stay friends, while at the same time keep things rolling with New Girl, all the while keeping them from knowing about each other. It's quite an awesome predicament.