Best C class on a *A RTW would be AirNZ LHR-LAX.
Next best option IMHO LX C via ZRH and then perhaps as a third option SQ FRA-JFK (Spacebed flight which is still better than LH C).
New UA C isn't too bad either. I flew them on IAD-FRA on a 767.
To the US I usually fly BA Club World ...