Try Langham in Mong Kok, it is true 5* luxury and has a great spa but at half the price of the other 5* hotels. The reason: location (Mong Kok is a poorer chinese part of the city). Think Times Square. The hotel is part of a really well done modern sky scraper (vertical shopping mall with a dizzying atrium and an escalator that almost qualifies for a Disneyland ride). Book a deluxe room or a suite (should be possible for USD 400) and you will be thrilled.

If money is no object, the Peninsula is the best hotel in HKG and maybe the best in the world (certainly in the top 10). But prices have gone way up recently, you are looking at USD 1000 per night for a nice stay at the Pen.