I had an original mini 1 cellular (and at the same time had an iPad 4). I went travelling around South America and took the mini and absolutely loved it, the form factor was perfect. I only used the iPad 4 when I was at home as a very basic laptop replacement (large screen internet browser!)
Last year I sold both and went for the Air thinking it would be the best of both worlds.....it wasn't. It still felt too large to carry around and feel truly portable, and holding it with one hand and tapping with the other always felt uncomfortable and too heavy - the only way I was happy using it was laid on a table.
So this year I've sold the Air and bought a cellular mini 3 64GB, which I love. It's got (almost) as good a screen as the Air had, and is so portable I can take it anywhere. For me the only advantage to the larger iPad Air is screen size, which isn't that much bigger and (I feel) you give up too much in portability to make it worthwhile. (However I am tempted in having an Air 2 as well purely for basic web browsing at home with it's 2GB of RAM!)
So for which one to choose..., if you value portability over screen size, plan on still using it standing up or walking round - go for the mini 3. If you're mainly going to be using it sat down at home or in an office, go for the Air 2.
This is all purely my opinion by the way!
