It's going to be Airbuses. Airbus will do whatever it takes to keep USAirways as a customer for these future widebody aircraft. Boeing will not likely budge much since they already have orders out the wahzoo for the 787.
Airbus will offered huge discounts, make interim 330s available to provide any needed lift, and probably pay part of the operating costs on the 330s to make up the efficiency difference with the 350s until they are delivered. Airbus can't afford to let this get away, and Boeing can.
This will probably tie into the narrow body orders, which will almost assuredly be 320 series aircraft. Personally, I'm astounded that any east 737s are being painted in new livery. I figured they wouldn't make the investment for airplanes whose days on the property are numbered.