I travel with 3! I use the 12.9 when i fly 1st class thanks to the extra space but will bring out the 11 when just travelling business class. I have the mini as back up if im flying coach. I love how apple thought this all the way through.I didn’t have a problem using my previous generation 12.9 on a plane, though, for gaming or typing on ASK.
That said, for quick and easy reading, I would grab the Air 2. But when settling in on a long flight, I’d bring out the 12.9 (yes, I sometimes travel with two iPads). On my upcoming trip, I won’t work much, so I’m just taking my new 11.