Thanks. Your list of pros and cons is basically what I'm weighing up.

QF giving lounge access in the US where AA doesn't seems counter intuitive, but that is an important benefit for me. I often arrive at airports with plenty of time to spare, so I use lounge facilities extensively.

I'm trying to find out if my employer will fund J fares for US domestic sectors ~3hrs, or whether they'll argue for Y as it's less than 4 hours. If they won't fund J, I think that this will add to the pros for AA.