The journey on the tube wins. It is direct, very cheap (£3.10 using oyster or contactless) and would be about an hour, but somehow always feels longer. It is likely to be the quickest option - traffic congestion (which includes at the weekend) in London has got significantly worse in the last year. Using the (painfully express) Heathrow Express could - in theory - shave a few minutes off, but only if you arrived at the platform at the right moment. As these only run every 15 minutes, add in waiting time and the time saving evaporates. Changing from HEx to tube at Paddington is a faff.