IME about 9 times out of 10, flights coming into LHR loop around over the city from the north. They circle out above East London and swing round over the south before approaching LHR from the east. This would mean that the seats with the best views of central London would be those on the left-hand side of the plane, or the K seats. This is not to say that the view from the A seat will be bad, but it will IMHO be better if you're on the left-hand side.

Occasionally the winds are such that flights approach from the west (over Windsor) in which case I've found that the side of the plane is unimportant.