I find facetime to have better quality video and audio.
As far as an ipod touch or and ipad 2?
The dual core doesn't matter if facetime is your main reason to buy, and an ipod touch can be a lot less expensive. However, if your going to get an ipod touch I would wait till next month, new dual core ones are likely to be announced.
Honestly, if money isn't a problem though, the ipad 2 would be a great buy for your dad.