I am confused... Please just tell me which London Tube card to buy
 

I am taking my first trip to London and plan on doing a lot of sightseeing within the city. I have been looking at travel card vs. Oyster card and have no clue which is the best option for me. I am hoping that an experienced traveler can just tell me exactly what to buy. I prefer to buy it online and take it with me to avoid any hassle or time consumption once I arrive.

I arrive in London on Friday afternoon at St. Pancras station via Eurostar train. My hotel is on Park Lane, near Hyde Park. I will be in London through the following Wednesday morning (6 days) and will depart for home from Heathrow. I would like to do a lot of walking while I'm there so I think I only need a pass for Zone 1 with extensions for Heathrow?

Can someone just tell me the best option and what exactly to purchase? Thanks in advance!!!

There is minimal time consumed when purchasing your Tube transportation upon arrival at St Pancras. And there is no need for confusion for what to buy.
Just walk right up to the ticket seller and say what your plans are. You will be sold exactly what is best suited for your travel needs.
In a matter of minutes you will be on your way.

As you are arriving at St Pancras then just get a 7 day zone 1-2 Travelcard.

If "I does mean "I" then go downstairs to the Tube booking office and get it on Oystercard and add on some money for the trip to Heathrow.
If I is "we" then get the Travelcard from the train booking office in the main station so as to take advantage of the offers on daysoutguide.com - you'll then have to pay a separate extension fee for LHR when you leave for the airport.

Agree - 7 day travel card is your best option for unlimited travel.

If you are two people and the days out guide above has things you want to see for 2for1 then go to the national rail station (not the tube) and buy a paper travel card for 7 days (it will be orange).

If its just you, go to the underground station and get an oyster card (£5 deposit you get back when you return the card) and load it with a 7 day travel card.

There's little (actually: none whatsoever) point in buying cards ahead of time - especially in your case. BUT there's a great deal of point in avoiding buying a Travelcard or an Oyster from the ticket office you come to if you "go downstairs to the Tube booking office".

Several hundred people hit those four selling points (there are more at that point, but they're electronic and we all know how incapable the French and Belgians are at dealing with machinery, so they take about 2 hrs each) simultaneously as each Eurostar arrives.

Assuming you want an Oyster, as soon as you see the queue snaking back towards you as you go down the stairs to it, nove to the far left of the stairs, and walk past the queue and the ticket office, following the signs for the Piccadilly Line. About 50 yds later, there's a larger ticjket office with a (practically always) shorter queue. Buy the right ticket (having previously determined whether you want Marble Arch, Green Park or Hyde Park Corner tube station, because that determines which line you now take) and go about your business.

If you need a railway travel card, it's quickest to go to the Midland Mainline office at St Pancras, not Eurostar.