At the risk of sounding like VK (whose advice I appreciate) there are some cracking deals on ba.com right now. I’d connect over LHR outbound but chose the direct AA flight to DFW with their new business. I agree that pre clearance in Dublin is hard to beat but as you’re connecting you’ll have to muck around with security again and I feel it much better to have the longest flight finish in your destination.
For the return I’d be tempted to go the same way due to the quality of the new AA business product, although via ORD on AA direct into Dublin is what my head is telling. 6 across angled seats though in business.
Price was under £2k ex Dublin and not 1 flight on BA.