As I've mentioned in other threads, the 787 would be nice, but the A350 may turn out to be the smarter deal for US. As an early A350 buyer, and the only one from North America, US is probably in a position to negotiate a VERY favorable deal with Airbus. Plus, if an even better deal is made on some A330 leases, it's a huge win for US...especially since those new A330s would likely start replacing the 767s much sooner than US could hope to have a 787 on property.
Rarely does an airline like US have this kind of leverage over Airbus or Boeing, the SandCastle would be foolish not to take advantage.
It will be interesting to see if Airbus also gets the narrowbody deal - of if that goes to Boeing.