What's the cheapest Travel card or ticket to buy for travel on London public transport (Zones 1 and 2 only)?

Please answer the questions in relation only to Tube, bus and Docklands Light Railway travel in Zones 1 and 2.

Warning: this decision tree will no longer be accurate when fare prices change. Please contact Improbulus if you spot any errors in this decision tree.

Created by Improbulus, A Consuming Experience, based on data from the graph by Neal Lathia - see his blog post which summarises the 2011 research paper from which the data was derived, by N. Lathia, L. Capra on Mining Mobility Data to Minimise Travellers' Spending on Public Transport (links to abstract and paper are on his publications page).

Produced using the Interactive Decision Tree tool by Warren and Josh. Thanks also to 24 Ways for the info on how to use Google App Engine to host this.