Skype or Facetime for calling from US A. To Europe?

We're going to be in Europe for 2 weeks in September and want to know the best (and least expensive!) way to keep in contact with our kids at home in the USA We use Skype on our PC, but now that the kids have iPhones, we were thinking that Facetime might be an option. Any help here would be greatly appreciated!

Skype!
I'm belgian but I live in the US. I talk
to my best friend all the time via skype
and it works well.

You can use facetime, works great over Wi-Fi and even internationally is free.

Either or would be fine. I'd use FaceTime personally though.