If staying overnight near Paddington, the morning Heathrow Express can be the most reliable choice

https://donovanoxeu003.trexgame.net/how-do-i-get-to-heathrow-terminal-four-step-through-step-routes-and-tips

If staying overnight near Paddington, the morning Heathrow Express can be the most reliable choice, beating rush-hour road traffic across west London.