Go USAir! I just came back from a FRA-PIT-LAX-PHL-FRA trip with them and I have to admit that they offer the best Y class service over the atlantic!
When I booked my flight, I've chosen USAir more because I could not avoid to fly them (booked just 3 days in advance), since I was until then a very loyal LH / United customer on transatlantic flights.
But what USAir offered was far superior to anything I've seen before on US Flights, with very friendly ground personell at FRA, friendly flight attendants, the by far best in flight entertainment system of any US carrier, with video and audio on demand in Y class. The A330 (flew N673UW east- and westbound) is a new, nice, clean and of course very quiet aircraft. It just feels like being on a LH A343, just a little more powerful and with better inflight service.
US domestic service was quite okay, but not outstanding. Would it be possible to apply dividend miles on my Miles&More (LH) account, I would prefer USAir over United any day!