I recommend that you go with the assured seats.

I bought 2 tickets for 2 international trips last August for travel this April. My husband and I are both EXP. We were cleared for upgrades one way on each trip. AA did not open up space for upgrades - despite the cabins being wide open - til about 10 days before the trip. I am much less sanguine about upgrades after that experience.

I suspect my experience about AA not opening up space for upgrades would mirror what you would experience waiting for J award space to open up.