Air New Zealand
I've flown R/T Los Angeles to London on Air New Zealand and have found the service to be truly excellent.
LHR > LAX / ANZ Flight #9835
LAX > LHR / ANZ Flight #2
That being said, you will want to fly in Premium Economy or better as the back end of the Boeing 777-300ER can only be likened to a packed sardine can. Nevertheless, the inflight service in Economy is still quite good.
Once in California you can fly intrastate LAX > SFO/SAN or on just about any domestic airline (United, Southwest, American, Delta and more)
Have a great trip!