Among all the laptops I had and used over trips, the MBA 11" is the only one that was really fine in all economy class seats. I did not have a 12" rMB and that one should work too. My current 13" MBP (2017 nTB model) fits only in more spacious than average Y seats or in seats that do not recline. Otherwise, I will just use my iPad Pro 11" with magic keyboard (which does not support all the things I need to work on, but at least it can keep me productive during flights).
Based on this, I would either get a 14" and expect to work only on some flights, or just get a 16" and not expect to work on any economy class seat.
Based on this, I would either get a 14" and expect to work only on some flights, or just get a 16" and not expect to work on any economy class seat.