Elizabeth line

Pros

• Take the Elizabeth line not the Heathrow Express. It goes to the same place, is 10 mins slower but half the price.
• Elizabeth Line is much cheaper and hardly any slower.
• Personally I would use the Elizabeth line whenever possible, especially if you have luggages.
• form Farringdon, you can do elizbeth line to tottenham court road, (front of the train) or Bond street (back of the train and stroll down to Piccadilly.
• Elizabeth line is fully accessible and has AC!

Cons

• Ignore any comments advising to take the Elizabeth Line. This is more expensive and takes longer to reach any sights you'll be interested in.
• There are faster routes via Elizabeth line but you'll need to then change in central London.
• The last Heathrow Express leaves Heathrow at 11.55, which means there's a very good chance you'll miss it. Ditto the Elizabeth Line. That means you wouldn't be getting to Paddington until well after midnight.