Abbey wood into london - cheapest way

Sorry if this has been asked a million times. I have had a look but cant seem to find any discussions on it .

going to abbey wood site for around 2 weeks. Will be travelling everyday into london for all the tourist attractions. A ticket everyday, oyster card or one of the types of travel card....are there different types? 

The website isnt that helpful, but then i am a bit thick. Does anyone from experience know which works out cheapest? Thanks