Out of all the video chat that I use, FaceTime is the best. If you've used it, then you know from experience that it's just way easy and the quality is really good.
If you've used any of the other video chat software like fring and Skype, then you know that FaceTime is simply better. Seriously. I use fring and Skype on my android phone and Skype on my notebook. If I had to choose only one video chat program, it would be FaceTime hands down on my iPhone or iPad 2.
Of course FaceTime only works via a wifi connection.
Skype and fring works via 3G and 4G as well as wifi. Skype and fring also work cross platform. So I can use Skype or fring on my iPhone or iPad, and video chat with someone using an android phone or tablet.
There are pros and cons for each program / app.
If I were to stack rank my preference.
1. FaceTime when possible.
2. Fring when chatting iPhone to android.
3. Skype when chatting android to android.