I've only been to London once. It was early May and gorgeous: great weather, spring flowers, not many tourists and lots of things to do.
I have a chance to go back this year, either in the fall (Sept or Oct) or early December. Considering the weather, scenery, crowds, and things to do -- which would you choose?
If it helps your recommendations, I'm a photographer, so getting beautiful shots of the city is important. But this is a vacation too. I love to explore the city, shop, hit the art galleries, people-watch, and go to the theater.