Obviously "best" is always subjective and depends on the particular person, but...
Having done 1-day stopover trips in Hong Kong a few times over the past few years (including a 22 hour stopover there 2 weeks ago!), my vote would be for the area on one side or other of Victoria Harbour - either the Kowloon/Nathan road area on the north side, or Causeway Bay/Connaught Road area on the south.
Both of these areas have excellent access to the Airport via either the Airport train (quicker and more predictable, but a little more expensive at HK$100 each way) or via bus. Both have access to the harbour, including various tourist favorites like the Star Ferry, The Peak Tram, shopping on Nathan Road, the Temple Street Night Market, etc.
Public transport in Hong Kong is very easy to use, and regardless of which side of the harbour you end up on getting between the two sides is easy. Taxi's are also relatively cheap - a trip up to a few kilometres will cost you only HK$20 (about USD$2.50) so even if your hotel isn't right next to the train stations it's easy to get around.
There are obviously countless other areas of Hong Kong you could visit, but unless you've been there before and already seen the sites around the harbour area then I wouldn't suggest going anywhere else - especially given your limited time on the ground.
If there's a negative about this area (and all of HK to some extent) it's that hotels can be relatively expensive. There are cheap options available, but make sure you read up on the reviews on sites like TripAdvisor as some of them can be fairly poor quality. Unless you're staying in a 4+ star hotel you can expect to get a small room little larger than a bed, most likely without a window - but for such a short trip that should be all you need!