Many of the UA flights are now showing up as US codeshare, and that will probably expand into the future. With US also joining *A in the near future, I'd probably go with the US flight on the Airbus 330 (if possible, I'd rather have it and not the 767). One note from many of us that have flown through PHL -- plan for checked baggage to potentially get lost/delayed and have some stuff in a carry-on. They've had periodic major issues with the baggage system in PHL.