As for recommendations for tourists, Oyster is great, but, there's really no need, a contactless bank card is capped at the same day and week rate as Oyster.
I've been commuting for the last year on my bank card, it's not the most financially efficient way, but it's not a lot more expensive (than a pre-paid pass).
Also bear in mind that a bank card will take ~2 seconds to scan at most stations' gates, versus milliseconds for an Oyster. It might seem trivial but at London rush hour it's an annoyance for you and everyone else.
One thing people also don't know is that at most stations, your card won't scan if you're standing between the gates, step back and scan or you'll just hold everyone up until you give up and walk away.
It's designed this way, I imagine, so that you don't scan while someone is still paying through the gate and have it close on you before you pass through.