Travel card or Oyster card?

To be honest, the cheapest and most efficient is to just use a credit card, or one loaded on a device (Phone or Watch) to tap in and out as you go.

You will automatically get the cap each day (or week if that applies) and no paying 7 GBP for an Oyster card, no calculating what to load, no worries about getting a refund of money not used, and no time standing at machines figuring it all out.

Trips to multiple zones, or from/to the airport are applied to the daily and weekly cap when applicable, so you can travel where you need to.

Others do love their oyster cards, fine if you already have one, but for those that do not, it just is not needed.

A travelcard can be for any 7 day period, but has to be loaded onto an Oyster card. The Oyster can have both cash and a Travel card on.
It is the contactless cap which runs for Monday to Sunday.
Uber boat fares are NOT included in the daily/weekly cap or with a Travelcard.

Paying the boat fare to Greenwich costs £10.80 each way on the app or £16.20 at the pier, with a Travel card it is £10.30 extra each way.
If you were paying at the pier you would actually buy a day rover for £29.55 each or £59.20 for a family of up to 2A and 3C.

A credit card wouldn’t be the cheapest way if your bank charges international exchange fees. Oyster would be best, load it with the amount you want on it, you can check the balance anytime at any tube station.

in the case that Robin Z mentions about your US bank charging extra, remember that the Oyster costs £7 each to buy, every time you top up will incur charges too.

Using a contactless card the card is only charged once a day if the same one is used all day and all week (for the week cap). So that's only one extra US charge if the bank charges each day.

Do those fees exceed the £7 purchase cost of the Oyster each?

An Oystercard is a vehicle for storing travelcards or pay-as-you-go funds. Paper 7-day travelcards are no longer offered. If you want a 7-day travelcard, you need to load it on an Oyster card.

If you load a zone 1-2 travelcard on your Oyster and it can start any day of the week. You can also load pay-as-you-go funds. If you travel beyond zone 1-2, the system knows to deduct the extension fare from your pay-as-you-go funds.

The main difference between using a contactless card and an Oyster are:
1) They Oyster card costs 7 GBP
2) The weekly cap for contactless runs Monday to Sunday. A travelcard can cover a different 7-day period. The cap is the same.
3) You have to stop at a ticket machine to buy your Oyster and load your travelcard or funds onto the Oyster. With contactless, you just tap in and out.

Honestly, I don’t think buying an Oyster and loading a travelcard will save you much (or any) money in your scenario when you factor in the 7 GBP fee.

Note that Oyster cards will be £10 to buy from 7 September. They are really trying to make them unattractive for the visitor or casual user.

A credit card wouldn’t be the cheapest way if your bank charges international exchange fees.

This is false. Credit cards exchange fees are around 1%, some cards charge a Foreign Transaction Fee (FTF) of 3% of the charge.

First, to recoup the 7 GBP Oyster card cost would require you to travel and cap out on the underground for about a month.

Second, I imagine when you buy the Oyster card, and load it with some amount...your card charges that same conversion fee and the FTF...so you essentially never "recoup" that 7 GBP (soon to be 10 GBP) fee.

A good point made by Paul - by the time you arrive the Oyster card charge will indeed be £10, not £7.

"credit card wouldn’t be the cheapest way if your bank charges international exchange fees"

You're going to have to load credit to you Oyster card anyway, so can't see how it would be more expensive to use contactless. And if your bank charges a foreign transaction fee, you really need to change banks. Alternatively you could use a stored value card like Wise or Revolut.

I bought an Oyster card in 2018. I have used it on 4 trips since then and been happy with it. I can leave it in an easily accessible pocket and not worry about losing it like I would a credit card. I have my senior railcard loaded on it and that gets me additional discounts. I load a travel card on it if I am staying in London long enough and planning to travel around a lot. I use a credit card that does not charge foreign transaction fees to load funds onto the oyster card. I usually do that only once based on an estimate of my travel plans, but it doesn't matter if I top up again because the fee is a percentage of the amount of money spent. I'm happy to leave a little money on the oyster card for the next trip. In fact, I hope I left a lot of money on the card from my summer 2024 trip. I'd rather be holding pounds than dollars right now. I have 36 pounds and 30 pence cash left over also. Wish it were more.

Just tap in and out using your debit or credit card. So easy and no need to pay £10 for an Oyster.

I’m with Paul - and anyone else encouraging you not to bother with an Oyster card. Load your debit card on your phone, tap in and out with the same phone every time, and the system will calculate the cap, etc. It is soooooo much easier than hassling with lines to “top up” and trying to calculate things in your head and trying to find a working ATM if you for some reason want to top up with cash instead of a credit card (presumably because you are worried about fees?) etcetera etcetera.

If your travel budget is so tight that fifty pounds or less in extra fees and charges will make a difference, I would be surprised. I also think that not having the hassle of mentally wrestling with all of these calculations would be worth a few quid - just for the peace of mind. Tap in! Tap out! So simple! :-)

Oh! And you didn’t ask, but since you are staying near Sloane Square, I’d encourage you to think about mainly using the bus to get around. It is CHEAP as chips, and you get to sightsee along the way to your destination, rather than go underground like a mole and miss all the cool stuff you can see from a bus.

When you are in central-ish London, the bus is rarely more than a bit slower than the tube, and the 10 minutes here or there that you might save on the tube is more than recompensed by the money you save on the bus, IMHO.

Notice that all the responders who mention ATM cards are based in the UK. Be careful with that. Many of us based in the US have left the greedy large banks and chosen a local credit union. I have never heard of a US small credit union that does not charge a foreign transaction fee for all transactions on their ATM cards. I’ve seen advertisements recently for “travel” checking accounts from online banks but I cannot see an advantage in establishing an ongoing banking relationship with them.

Just a reminder, 1% of $30 dollars is 30 cents, 1% of $10 dollars done 3 separate times is 30 cents. That is what the typical foreign transaction fee is when you tap your ATM card (costs more to withdraw cash). I have dysgraphia and am not going attempt the 1% of the fee in dollars required for a pay toilet. The answer is “tiny.” If you use a credit card with no foreign transaction fees the answer is $0. No fee. None. If you are going to travel often you need a credit card with no foreign transaction fees. Capital One has some that charge no foreign transaction fees and no yearly credit card fee.