Don't forget, you can also redeem miles on AA, so Im sure you can get some use out of them. I think the driver of choice should be earning miles rather than assumed ease of redeemption availability on 1 route. As the others say, SFO - LHR is very popular.

Personally, I would channel all my business through one scheme as far as possible, as the status is as useful as the miles, particularly in the US to bypass security queues. It depends how much you fly though. If you travel to London a couple of times a year with several domestic trips, I'd focus on exec club, switching domestic flying to AA. If however you are flying more domestically, then I'd switch your transatlantic business to virgin. The only drawback of their scheme is that there are not affiliated to the big alliances, but if you only fy Virgin than that doesn't matter.