We recently faced this decision too and opted for the Air. This was to get the better display, camera and two generations newer processor (that make it faster and will hopefully give it a longer life).
The price difference is quite high and the Air will also force you to the more expensive 2nd generation Pencil (if that's relevant).
I think the base iPad is really capable and good value for money so I'd look hard at the differences and what they're worth to you personally; I doubt you'd be disappointed with the base model.
Hi Robin, I have 3 iPads, one is the first iPad Pro 12.9”, the other two are minis, one with cellular capability (never used that part as I bought for my folks who didn’t wanna know) and the other mini is a rather new one that uses the pencil, 1st generation pencil as that matches my big iPad Pro. I don’t use the pencil that often but when I do, it is absolutely needed for drawing programs and very useful for signing important documents which aren’t good signing using one’s finger! As there are so many versions on the market I think you’re really best to go to an Apple store and have their geeks give you facts to help your decisions. If that’s too difficult to get to an Apple store, I’d recommend watching YouTube videos explaining the features and uses of the different iPad Air, and iPad Pro’s. Good luck.
Robin Samways 