Oyster Card or Travelcard

First question, do you want to take advantage of the 2 for 1 offers:
https://www.tripadvisor.co.uk/Travel-g186338-c195600/London:United-Kingdom:2.4.1.Travelcards.Step.By.Step.html

You say I and we. How many is "we"? Adults? Kids? Kids' ages?

You do mean Stratford, East London - where the Olympics was help and where a huge and very crowded shopping centre is - or do you mean Stratford-upon-Avon - where Shakespeare lived and loads of tourists go, and just down the road from Warwick Castle?

Nigel, just two adults traveling and we may want to do both parts of Stratford. We are there for several days and I haven't figured out completely what we will be doing.

harleydonski, I actually didn't know about the 2 for 1 deals. I may want to do that.

When you say "both parts of Stratford," it's unclear whether you realize that Stratford-upon-Avon is approximately 100 miles northeast of London. To get there by public transportation, you'd have to go far outside the range of the Oyster card and Travelcard.

See
http://gouk.about.com/od/uktraveldirections/qt/Lond2StrafordAv.htm

epltd, my plans are not final so we could go to both areas but not in the same day obviously. I was using Stratford as a border as to how far east we would travel. Stratford is not the focal point. I'm just wondering what the best choice will be for a 13 day trip in terms of paying for transit fares.

we may want to do both parts of Stratford

ketakechi, Stratford East London and Stratford-upon-Avon are two entirely different places, over 160Km apart. Stratford, East London is accessible by the tube central line, and an Oyster card is valid. Stratford-upon-Avon is in Warwickshire and you need to get a train there from Marylebone station which takes about 2 hours. Which do you mean?

I've updated my post to clarify Stratford East London. I know anything outside the city will require other means of transit.