What would be the best transit option?

We're going to be in London for 10 days (excluding the days we're arriving and departing) and will be using the Tube for all of them, basically in areas 1/2 and off-peak. I've been researching different payment options—Oyster card, 7 day Travelcard, Travelcard loaded onto an Oyster card—and have gotten thoroughly confused. What would be the best deal for us?