1. You need to be on a BA-operated and ticketed flight to UUA from an I-class fare.

2. Seat selection depends on metal, not ticket. Free for a bronze one week out on BA, free at any time on AA (as well as 50% off Main Cabin Extra).

3. You'll earn more tier points on AA, but fewer Avios in business class. (AA first class earnings are the same as BA business class earnings, so this only applies to the TATL legs).

4. If you routed DUB - PHL - LAS on AA metal, an AA ticket would give you no qualifying flights. If you routed DUB - LHR - BOS - LAS however then as DUB-LHR and LHR-BOS are only operated by BA, you'd have at least two qualifying flights on each of the inbound and outbound.