Seems like the refurbished iPad Air 2 is the best value now, more than ever.
I haven't decided yet, but I think the best buy is the refurbished Air 2. I could even find a brand new one from an Apple reseller or other channels.
My only concern is that Apple could decide to remove Air 2 from the list of supported devices in future iOS releases sooner than the new iPad. Of course it is something we cannot know today, and I'm confident Air 2 will receive iOS updates until 2019 at least.