Bangkok is a wonderful city, but can be a little difficult for the first-time Asia traveller, what with tuk-tuk scams, taxi scams, beggars, touts, etc.. I'd definitely recommend Hong Kong, for a number of reasons. First and foremost, it is absolutely unique -- a rather schizophrenic mix of Chinese and British culture, unique in the world (and very different than, for example, Tokyo, which also mixes western and Japanese culture but in a very different way). If you want "exotic" there is plenty of that to be found in Hong Kong -- lots of Budhist temples, "locals" restaurants, nearby fishing villages, etc. There is also plenty of what you called "Asia light," an Asian experience that takes into account (but doesn't necessarily pander to) westerners.

As another poster mentioned, there is excellent ferry service to Shenzhen and Macao (there are casinos in the latter). There is also an express train that puts Guangzhou a mere hour train ride (on quite a comfortable train) away.

I think you can easily spend a week in Hong Kong (I once was there for business for nearly a month).

As much as I enjoyed Bangkok, I find Hong Kong to be one of the most exciting cities in the world, and I'm looking forward to going back (we're going to Cambodia over Christmas, with a stop in Hong Kong on the way back to visit friends and relatives).