Is an OysterCard worth it for occasional 1-day visits from outside London?

If you've got a contactless credit or debit card, you don't need an oyster card. Since September 2014 you can just tap in using that contactless card everywhere you can use an Oyster card, and it charges you the same rate as an Oyster card, with the same daily capping policy.

(there are other high tech "contactless" options too like NFC smartphone apps that work the same way, check this TFL list if you like being unable to travel if your gadget's battery runs out :-) )

Basically, since this was introduced, there's no reason to have an oyster card unless:

• You don't have a contactless card or it's a card where your bank might charge you to use it (e.g. for a non-UK account)
• You're a commuter or regular traveller with a weekly, monthly or yearly travelcard (which still need to be assigned to an oyster card).
• You're under 18 and can get one of the children's cards with lower rates.

...and there's no reason to get a one-day travelcard unless there's both a) a special offer on travelcards (e.g. with a rail or tourist attractions ticket) that makes it cheaper than the oyster/contactless daily cap (e.g. £6.40 for zones 1-2, £4.40 for buses and trams only - regular 1-day travel cards are £12) and b) you'll need enough transport that it's worth it (e.g. three tube journeys if it's ~£6).

Be careful to use the same card for all journeys, as it caps it at or below the cost of a travelcard (just like an oyster card does), meaning this is better than a day travelcard: you might spend less this way and can't spend more. The system is designed so that oyster or contactless is never more expensive than buying a travelcard (unless you're offered a special offer), to encourage people to pay the fastest way which involves least queues, machines, staff time etc.

And beware of the dreaded "card clash" where multiple contactless cards interfere with each other, if, for example, they're all in the same part of your wallet and you tap in by plonking your wallet on the card reader. Keep the card you use to tap in and out on its own when you use it, and if you keep it in your phone case, turn NFC off on your phone to avoid the battery being drained by your phone constantly trying to talk to your card and getting confused that it doesn't answer...

Here's what TFL say, from the contactless section on their website:

If you currently use pay as you go [oyster card], travelling with a contactless payment card is a good alternative. You are charged adult-rate pay as you go fares, but you won't have to worry about running out of credit and could also benefit from daily and Monday to Sunday capping.

To benefit from capping you need to choose one card and use it for all your travel. We can't link the travel charges on your Oyster card with those on a contactless payment card.

...and you also save the £5 Oyster card 'deposit'.

Here's confirmation that contactless cards benefit from capping:

With a contactless payment card you can:

• Use pay as you go and benefit from daily and Monday to Sunday capping

(Monday to Sunday capping is a contactless-card only thing that caps a calender week at £32.10 for zones 1-2, other prices for other zones)

In my experience, no, the day travelcard is usually cheaper.

Depending on where you are going from, you might also find that you can get a railcard which makes it even cheaper still - such as the Network Railcard if you're in the area it covers, or the Two Together Railcard if you regularly travel with the same person. Both of these are £30 and get you 1/3 discount off the price of off-peak tickets, so usually cover their cost in 2-3 trips. [Note - I have no connection with either of the above schemes, except as a satisfied customer]

I wanted to add a comment to @user568458 answer but I don't have enough reputation points yet. Until recently I used contactless credit cards, but recently I have had trouble with this system. On one occasion I was charged an extortionate amount for a single journey (yes I 'tapped out'). On another occasion I have had the credit card stop working on TFL (it still worked in shops etc). I asked a TFL member of staff what was happening, and he advised that sometimes the TFL system has trouble taking payment from contactless cards, so it blocks the card from TFL. I now use an oyster card.

The likely answer is no, it would be cheaper to still buy a Travelcard from your local station. Oyster is slightly more convenient to use than a paper ticket, but not so that I would consider it worth spending more to do.

But this is something you can check by comparing the cost of current Travelcard with the equivalent return ticket plus the Oyster cost. Which for two zone one journeys would be £4.60, or capped at £6.40 for three or more journeys.

Depending on your location you may also be able to break up your journey by buying a return to a station within the zonal system and then using Oyster to cover the journey into zone one. But this does mean having to changes trains at that station, and in many cases having to exit then reenter the station so you can touch in with your Oyster card.

The likelihood though is that even where cheaper it would not be by enough to justify the added inconvenience. Although if you are on the Cambridge to Liverpool Street line then, in my experience, changing at Tottenham Hale for the Underground can be both cheaper and more convenient than going via Liverpool Street. So it is not a situation worth discounting completely depending on your particular route.

And unless you have a Railcard which can be added to an Oyster card, using a Contactless debit or credit card would give you all the same benefits as Oyster without the need for a deposit or loading credit.

So in summary it is impossible to give a definitive answer as it depends on your specific route, but it is likely that your current Travelcard is the best option for you. If not then using a contactless card would be marginally more convenient than an Oyster card for the same benefit.

Yes, a Oyster card saves a lot of TIME, not having to buy tickets or travel cards. It may also save you money, but not having to queue up for 20 minutes to get a tube ticket is of a lot more value to me.

The only time I would consider not using a Oyster card, is if I never travelled to London apart from on a rail ticket that has a very cheap “add on” travel card option. Some rail stations a small distance out of London sell combined all zone travel cards and rail tickets for not much more then the rail ticket.

Even then, it will depend on what tickets I can get from the machine without queueing at the train station.