The ideal size is what works best for each of us... might be the Air, the iPP, and for some , it may be the mini.
+1
It's all about how you use it. For me, if I was using it a lot of the go, and was using local transit, the Mini has a nice advantage there. If I was using it on a table most of the time or on a lap desk, the extra screen space makes the Pro interesting. But since I tend to be in the middle where I use it around the house and office, on the couch, in my hands, the Air has made the most sense.
I still like the idea of the Pro, but I found myself reaching for the Air since it just fit that niche of how I use tablets better.