United
Shame to see them go, was talking to a person this week who when from NY to London last month.
United from EWR-BHX-DUB $500 (return), they then flew with BA back to LHR. Flying direct EWR-BHX would of cost them $850 (return) for the same flight/dates.
An extra 6-7 hours flying/connecting to save maybe $250.
Strip the taxes, charges, op costs and Aer Lingus cut from that $500 you UA will have little spare change and if this was repeated by a high volume of passengers losses would mount. Given SN, LH, LX, EI etc all code share with UA it could be a common passenger trend.