I'd recommend focusing on two key aspects: the total duration of the journey and the options available in case of irrops. Comparing the routes, the AA route MAF-DFW-DUB seems to be a superior choice in terms of both travel duration and flexibility during irrops, as opposed to the MAF-DFW/PHX-LHR-DUB route.

Regarding the crediting of miles, it appears quite straightforward for you. For your son, the decision hinges on his intended use of the FF program. If he's aiming for status, BA might be the easier option for achieving and maintaining it. On the other hand, award availability generally tends to be better with AA, particularly if he plans on returning to the U.S. after completing his studies in Ireland.