What is the best way to get to the JW Marriott from the Hong Kong airport? We will be getting in at about 23:00.

At that time, you can still take the local public bus line A11 to Admiralty Station, Queensway Station and then walk along the Queensway for several steps to reach your hotel easily.

To back to the airport, you can walk to the RAVANA GARDEN Station to take the bus line N42 to the airport directly. The bus line N42 are only available at 03:50, 04:50 from YIU ON B/T Station, so I think the bus line at 04:50 is suitable for you. But when the bus will reaches the RAVANA GARDEN is hard to predict and you can ask your hotel staff to get a general idea.
If you think it confused, you are take a taxi for the airport.