I'm partial to the retina mini
I have both. Performance wise the Air 1 and Mini 2 feel the same to me. Both are data capable and on ATT
The mini is in my hands right now, and is 95+% of the time.
It's all about portability to me. Hope this helps....
Air, no question. The screen on the mini has an incomplete color gamut, resulting in inaccurate colors, which is a deal breaker to me. Even the Nexus 7 has a 100% color gamut(a device I also use a lot). I've had both the mini and the Air, and the larger screen is just more of a pleasure to use. Unless you're going to be carrying it around with you, get the Air.
I ended up buying the ipad mini 2. Let me say that the ipad feels great in the hands and its so easy to navigate around. I also used a friend's ipad air to compare and the air just feels too big. Also the mini came with ios 7 which is so much better than ios 8 in my view. Thanks for all your feedback!!