I will be in London for a week and can't decide whether it is more cost effective to get an Oyster Card when I arrive or buy a 7 day Travelcard. I don't want the Visitor Oystercard because the deposit fee isn't refundable. I've read all the info on the internet and am still thoroughly confused at this point. I will mainly travel in zones 1-3. However, I am also going to Warner Bros Studio which I know is near Watford Junction. I know that I can get a train from Euston Station there, but don't know if getting the Oyster Card is a better bet because I could use it to pay for my train ticket to Watford Junction. My understanding is that the Travelcard won't cover my travel there. Any suggestions would be greatly appreciated.