Wait until you're ready. If you're still using the term 'v card' then I have a clue you might not be...
Sex is great, I'm not gonna deny that, but you have your whole life to have sex (or at least until you hit the menopause and then it might be a bit more of an effort). But anyway, when you're young it seems like such a big deal and I remember being impatient too, but I can honestly say if one of you is not feeling ready for it, then it's going to suck.
And you know what's worse than not having sex? Having BAD sex just for the sake of it!
My second piece of advice is to try and act cool about it. I know it's tough when you've still got your v card firmly in your wallet or whatever , but don't build it up too much.
These girls want to get freaky? That's great news really. Lots of guys would like to be in your position. Just try to enjoy hanging out with your current girlfriend and if one night it feels right then go for it.
If she's only with you to have sex then turning her down won't do much to please her that's true... But then if she wants sex and you're not ready it doesn't sound like the kind of relationship you want to be in either!