On this point I would disagree with Pete - you are pretty likely to be approaching LHR from the east so you want to be sitting on the right hand side of the plane. If the weather is nice, you should get some lovely views over central London including the London Eye etc.

It’s certainly not guaranteed as the normal pattern does change based on wind direction, but ordinarily you would be coming in from the east.

[ETA: Note that’s for landing at LHR. For taking off it doesn’t matter so much as you’ll usually be getting countryside views which are nice either way. Sometimes you can get London views - notably as you turn over Hampstead Heath - but I’d more focus on the SFO approach for your return, if that’s at all predictable.]