Cost and time trade-offs
From central London the ranking is simple. The Piccadilly line is the cheapest rail option at about £5.90 and reaches all terminals, but it makes many stops and is the slowest. The Elizabeth line at £15.50 is roughly twice as fast and runs direct through the middle of London, which usually wins once you count the second fare you would pay after the Heathrow Express drops you at Paddington. The Express only becomes the value pick when you book the £10 advance fare 30 or more days ahead and Paddington genuinely suits you.