A.Lee wrote:
Myself and a friend will be in London for a day in a few weeks time, and
would like some advice on if, and which, travelcard we should buy.

If you are traveling by train the cheapest option may be to get an
out-boundary Travelcard from your home.

If you will only be traveling by LU/DLR/Bus on the day (no National
Rail), then Oyster will be cheaper if you don't consider the GBP 3
deposit. You can re-use it or cash it in.

If you don't want to bother with keeping or returning your Oyster card,
then the Travelcard will be cheaper.
--
Michael Hoffman