You can get a slightly better deal using contactless when it comes to the fare capping. Oyster does daily capping, with contactless you can also get weekly capping. Also with Oyster you can add travelcards (7 Day, Monthly and longer period).
https://tfl.gov.uk/fares-and-payments/fares
http://content.tfl.gov.uk/adult-fares.pdf
So, it depends on your type of journey. For random journeys, it doesn't really matter. If you are using it for work for a long period, then an oyster with a travelcard is likely best, as you can register it and recover the travelcard if it is lost and also employers often offer travelcard loans.