Apple this week announced their new iPad (and iMac) lineup. The most significant addition was the thinner top end iPad Air 2 with its new processors (A8X and M8), communications (wi-fi ac supported) and upgraded camera. But the iPad Mini 3 announcement was essentially a name upgrade with no change in form factor and/or hardware except for the addition of Touch ID.
I welcome the Touch ID which makes projector use much better. Up until now I have had to disconnect or blank out the projector screen whenever I needed to enter my security password. However I do not think this single hardware inclusion is worth the USD100–150 more for the same “older” versions that do not have this one functionality.
So save yourself a lot of money by purchasing the iPad Mini 2.
The iPad Air 2 however is a different beast with some new core hardware. So there is no contention as to which to buy if you need the larger form factor of the iPad Air. The upgrade is significant in taking advantage of the latest technology.
So if you have deep pockets then iPad Air 2 is the one to buy.