I would take Envoy on the A330 over F or C on the UA 763, I would also take Envoy over C on the 777, but if you can confirm a F seat on the 777 then I would definitly go that route. Basica Rule for me is that Envoy on the A330 is better than UA C on the 747(except for row 15) and the 777, rule number 2 never fly UA 767 F,C,Y+,Y period.