I would definitely go for the 1am flight. I usually stay awake as long as I can so I'm super tired and have the best chance of sleeping a longer period. Usually when I get up, the flight is about 4 hours out. Getting into HK at 6am is also much more productive than 2pm, good time for an early dim sum breakfast or a long shower before work.

Also, I always feel daytime flights are a huge waste of productive time.