our decision on that nov-weekend-trip was the tube:

- we had only handluggage
- arriving Saturday / leaving Sunday: no workday-rush hour
- the workday from 9AM valid ticket (go as you please) is 24 hours valid on weekends (for follow up sightseeings), I think it was about 6£ for 2 days from LHR-zone (including riding unlimited doubledecker-buses on the top - for me the even better thrill than the tipical London taxi.
- reminding me of my 9 months as a student trainee in London in 1963
- gets you right into the real London local feeling
- direct Piccadilly line/stop to our Knigthsbridge hotel (Connaught).