Originally Posted by
GatoVolador
if IB gives you the lowest, I'd buy the ticket through iberia.com, since you'll have the opportunity to select the seat you want (only for Business Plus travellers, so... J tickets), and moreover there is a field for AAdvantage cardholders identification. If not, bear in mind that you can already check-in through iberia.com and print your boarding pass one day (or two?) prior to the departure, which will allow you to select the seat (only if the issuer of the ticket didn't assign one for you).
If Iberia is cheaper, I would actually price it through AA.com as well. Last time I bought a ticket, I remember saving $75-$150 because AA wasn't subject to some special tax applied on foreign carriers (I think). This applied even through they were only selling a ticket.
I was able to call them to assign seats.