I would fly AA on the way there as it tends to be more timely (for your cruise). 2.5 hours is enough to do the transfer. I would probably try to call BA to change the business class ticket onto the outbound, since AA J is better than the old Club World cabin. You'd also still get UK passenger rights.
Return, I would fly the BA A380 since the upper deck is very comfortable, even in economy or premium economy. That will also preserve your UK passenger rights.