Vancouver is my most frequent long haul route so I've had similar concerns. I came to the conclusion that I would probably grab an UD seat on the LHR-YVR sector and select a seat in the OF cabin for the way back. I fly solo so OF offers more privacy and a bigger seat, I don't care about IFE but for the moving map. Plus 1A on a 747 is as iconic as the UD IMO.