The debate goes on. Which is the quickest way to get to and from Heathrow (in non-pandemic times)?
Three factors play an important part.
Are you with or without luggage? What time of day are you travelling? Do you want exclusive or public transport?
The first two are easy to answer. If you have gear there is probably little choice but do negotiate a fare, and traffic during the so-called 'rush hours' can be horrendous.
When it comes to public transport there are three choices.
The Heathrow Express is a fine service every quarter of an hour from Paddington, the journey to the central area (T2 & T3) taking 15 minutes and T5 three minutes later. But you have to get to Paddington and whilst pre-booked seats presently start at £5, buying on the platform costs £22. There is continuous wi-fi connections until you are into the terminal (which is also wi-fi friendly).
All the Underground (Tube) services connect to the Piccadilly Line but, say, from Bank there are 15 stops, it takes 65 minutes (1 hour 30 minutes from Cockfosters) and with the best will in the world it is not the most comfortable of rides. The Heathrow signposting could be improved. Prices start from £3.10 which is the same as the not well publicised Transport for London (TfL) Rail also from Paddington, poorly signposted and reached at the far end (west) of the main platforms. In time it will be replaced by the Elizabeth Line, the trains are very comfortable and taking 30 minutes including five stops at west London stations.