I recently faced that "dilemma". I am taking a relative (< 18) on their first trip overseas. At their age, they can certainly handle coach, but my recent "half-way across the Atlantic" trip to Iceland in coach told me that long red eyes in coach are painful as you get older (thanks to FT, it's been a while that I had to cross a large body of water in coach). While I want that trip to be a wonderful adventure for them, I don't really want them to think that J is the only way to do that. And I certainly wasn't going to book J for me and coach for my guest.

Fortunately the available UA E+ awards we so expensive that a BA Premium Economy award was the more economic option. So the trip won't be in lie-flat J, but there will still be some reasonable space and comfort... and a lesson that it sometimes pays to comparison-shop across carriers and cabins.