CX255 is primarily London based crew however last time I flew it was mixed based (ISM/SP/FP all HK based whilst all BC are London based). I generally found London based crew the best one out of all the outport crew.

For all my US bound flights I would only fly on HK based crew operating flights as my experience with SFO based crew (primarily 872/873) weren't exactly great! But each to its liking.