Well since everyone is voting for Singapore, I thought I'd stand up for Hong Kong!
Obviously it really depends on the person - are you a city person or more of a country one? Singapore is sleepy and 'provincial' (perfect description slim22). HK is a world city, with a great vibe to it. Sure it's more hectic, but that is part of city experience and appeal.
Singapore is much less sophisticated. I guess because it's come into its wealth a lot more recently, but also could have something to do with the paternalistic approach of government (remember it's a country that canes people if they step out of line). There is a level of antagonism against expats in SG that I don't recall in HK - again could be linked to newer wealth so residual inferiority complex (and I don't mean this to be bitchy at all, just trying to paint the picture).
I admit that Singapore is an easier place to live, but I honestly thought expats in HK were happier. I guess easy doesn't automatically make for happy. Both places have inexpensive home help, so in that sense they are both easier than in the UK. Maybe the difference is that in HK there is still enough energy to keep you going, but SG is soooo easy it crosses over into the field of boring, which can lead to other problems.
Being a 'dependent' in SG is worse as you have less autonomy than you would in HK. You will need your spouse to do everything official for you - even get you a mobile. As a fairly feisty woman, it has made me feel belittled.
Last few points in favour of HK: housing is definitely smaller and more expensive, but other things are much cheaper. Going out for decent meal and bottle of wine for example. The cost of alcohol in SG will make you weep. (Possibly why expats in HK seemed happier? They can afford to drink!)
And finally, the whole 'working girls' scene is very big in Singapore. It can make going out uncomfortable at times, and I promise I've never even been to the actual red light districts or buildings. In HK, beyond Wan Chai, you can easily avoid it.
So - there you have it: A pro Hong Kong vote.