Tour buses, London
Tourist Buses: Unless you have very limited time in London, avoid the tourist buses. They are quite expensive and you will find yourself getting caught up in massive traffic jams most of the time. It's best just to walk around or get the underground if you are travelling longer distances.
A wery expensive way to see London.
Fun Alternatives: Take the Underground to all the places the bus is going, it might take a little more time but much more cheaper.