Heathrow to Premier Inn at London Euston and Kings Cross St. Pancreas

To answer your last question first - it depends - where is your hotel? If you will be at the titled ones, bus or tube to Paddington station, train to Slough (rhymes with cow) change for the little shuttle train to Windsor & Eton Central.

By the way - in London a Subway is a place to get a sandwich or salad, or to walk under a road. If you want the Underground train that is colloquially called the Tube, not a subway.

First, there are 3 Premier Inns between Kings Cross and Euston station. They are: Premier Inn Kings Cross, Premier Inn St Pancras, and Premier Inn Euston. St Pancras splits the difference between the other 2. The easiest way to get to any of them from Heathrow is to just take the Underground- the Picadily line goes to Kings Cross. From there it's a block or 2 to the hotels- about 3 long blocks to PI Euston.

You want to access the Underground tube system, or buses to get around London. As mentioned, Subways are sandwich shops. The easiest system for your needs is likely the Oyster Card. Buy one for each of you when you land at Heathrow and load them with £20 or so each. If you run out of money on the card, top it up at a machine at any tube station. At the end of your stay either return the card and get a refund once back at Heathrow or keep it for your next trip.

The Oyster card does save you money, quite a bit of money. Returning the Oyster card was easy. We did it by machine at St. Pancras underground station. Not all stations allow you to return the card, but I imagine that the stations where you are most likely to end your trip will have that capability.

Hi from Wisconsin,
Let me highly recommend the Premier Inn that is directly across the street from the British Library.
1. great location, 2. absolutely quiet when your window is closed, 3. friendly, helpful, professional staff. 4. Pret a Manger cafe is nearby. 5. A couple really nice pubs on the opposite side of the block that the inn is on. One is named Mabel's, the other is The Skinner Arms. Filled with regulars. Avoid the Euston Flyer, it is fake and designed to capture the train travelers looking for a meal.
6. did I mention that the British Library is across the street, admission is free and the display of historic documents is stunning, and they have a coffee shop in the yard and inside.
wayne iNWI

"I am confused on London Travelcard v Oyster Card v Contactless Card in 2019. Are these just all ways to pay for subway travel or do they save you money on the subway?"

First, as said, in London it's called the Underground or tube, not the subway (and not the metro). And that's not just a pedantic point - a subway in London is an underground pedestrian passageway, so if you ask for "the subway" you will be directed to something entirely different from what you want.

All of these are indeed ways to pay for travel in London (Underground, buses, Overground, some trains, etc). They are indeed FAR cheaper than individual tickets (as in, half the price). Furthermore, the buses do not even take tickets - you need one of these to ride a bus.

Since you're only in London for 2 days, and not even two days together, you do not want a Travelcard (it might be advantageous if you're staying a week or more).

"From reading the forum I did discover that contactless card is a credit card and that US credit cards don't always work."

Both credit and debit cards can be contactless. If your card is contactless, it will have the "waves" symbol pictured in this article: https://en.wikipedia.org/wiki/Contactless_smart_card.

Most US cards are not yet contactless, but it is slowly being introduced. It is also true that even if you have a US contactless card, it may not work on the Underground. Furthermore, if you have fees for foreign use, these will be charged if you use that card for London transport.

"I have set my credit card up in google pay."

Google Pay should work, but make sure you can do it quickly, so you don't incur the ire of commuters behind you waiting for you to get the transaction to go through. If you're fumbling to get the right card of several on the account, or to get your fingerprint reader to work, you will definitely feel the "British reserve" melt away and be replaced by something far less pleasant.

If you don't have a contactless card, or if you do but it doesn't work on the Underground, or if your card will have fees for foreign use, or if you can't do Google Pay quickly, just get an Oyster card (£5) and load it with £15 or £20. Just tap in at the beginning of every ride, tap out at the end, and the Oyster computer will figure out the rest. If you run low, you can always add some credit. At the end of your trip, you can either get the Oyster fee and any remaining credit refunded, or can just save it for future trips (yours or someone else's). Note that in order to get the refund, you have to make sure you've used the same method (cash or the same credit card) for the card purchase and all loads and reloads.

Note that each traveler needs their own Oyster or contactless card or Google Pay phone - they're not shareable for this purpose.

Go to the source for transport info, which includes an interactive route planner and info on fares and Oysters:

https://tfl.gov.uk/

The phrase "contactless card" is confusing. I think most people do tap their cards on the card reader, although it is true that sometimes the transaction will register when the card approaches the reader. "Tap and go" comes closer to describing what I do (my Canadian card is good for up to $100 without further data.)
In an irritating reversal, the Underground Oyster reader will not take either of my credit cards. There is a warning about this in the section on Oyster.

I particularly like the one about the waves. I was stuck in Amsterdam when my credit card wouldn't work and paid a girl cash to buy me a ticket to get back to the airport. I'll check out my new credit card for waves. I've also found my debit card works when my credit card will not.

I picked the Premier Inn London St. Pancras because it had the best reviews and was the newest one.I had put the stops that the hotel suggested in my post above. It appeared to be a good location.

Thanks for the tips.

If you'd like to enjoy a cocktail in a lovely setting, walk across Euston Road over to the St Pancras Renaissance Hotel and enjoy the beauty of the Booking Office. You might also walk behind St Pancras to the Regent's Canal and on into Granary Square and the adjacent Coal Drop Yards.

You are across Euston Road from the British Library. The sir John C Rittblatt gallery aka the Treasure Room is interesting. https://www.bl.uk/british-library-treasures

Lastly, I'd get an Oyster card for each of you when you arrive in London. Easy Peasy. Return for a refund or keep till your next trip to London.