don't quote me but I am ALMOST certain that Stanstead has a coach service direct into central London, and stops at the end of my road on Bayswater Road/Notting Hill Gate (right by Kensington Gardens).
It could be Luton though, so CHECK.
If it does I would do that, because its direct and no changing, and the bus stop is ridiculously convenient.
However if tubs are your option, Liverpool Street is fine. However, to Bayswater means you have to take the circle line to go direct... and without complicating things too much the circle line no longer goes in a circle (LOL) so you would have to change platforms at Edgware Road, which I do not recommend to ANYONE. PLatform confusion hell. You'll end up in Heathrow.
Liverpool Street to Queensway is direct on the CENTRAL line, takes the same amount of time, and Queensway is barely 2 minutes further walk to the hotel than Bayswater. It's all very close together.