The quality of United's premium international service is limited by the attitude of the flight attendants, who are "primarily here for your safety" and not to provide service. It's a rare United FA who can compare with the attentive service given by Thai or Cathay Pacific. Regarding F versus C, I find United's Transatlantic F service to be just about identical to C except for the seats. Transpacific, on the legs with Asian FAs they do better.