I am not sure on the youth card. You can get a regular Oyster card at any tube station or Heathrow. I think there is a 3 pound refundable deposit.
Travel cards are for at least 7 days worth of Tube and bus travel so that probably wont be necessary unless youre going to be travelling around London for a week. They have cancelled the 3 day pass.
How many times will you be traveling on the tube?
You can get a refundable pay as you go Oyster card but that is only worth it if you use it about 2 or 3 times a day at least, because it caps off at a certain amount.
Not sure since it has gone up since I was there in November but it was capping off at 5.40 per day and a ride each way per single ticket was 4.40, so if youre only riding it once, you wont save any money.
Travel cards are mostly for people staying in London or surrounding areas that are riding the tube or buses alot each day.