I'll add another vote of endorsement for HK, with more than a decade here as an expat. Thailand seems to be less endearing each time I visit. If you love your bike then you'll need to be careful where you choose to live. Mountain biking is largely banned in the countryside, but there are extensive cycle paths in the New Territories, and big plans to extend these. Discovery Bay might be the place for you if you don't mind a ferry commute. September won't see HK at its most comfortable. Heat and humidity of New York in August, with a good chance of typhoons.