I lived in Singapore for most of my life and only recently moved to HK for 3 years.
The only attractive pt of HK is the higher salary and personally for me the fact that it has "winter" season with cooler weather also attracts me.
Other than that SG wins in terms of clean air, greenery, larger and cheaper (HDB) houses, better eductation and kids get to speak English at young age. Did I forget to mention the roads in SG are straight and much easier to manuver? I am one that is prone to car sickness and HK hilly roads are definitely not a plus.
Hk is more "traditional", crowded and dirty ( Mongkok, Kowloon places which I avoid) One of my top complaints is the lack of toilets in HK. Why are there no toilets in MTR?? you find in them in Japan, Taiwan, SG and yes even Shenzhen! This is something I cannot understand and find very frustrating as I always have a small baldder.
A minor complaint from a Singaporean will be the lack of spicy foods and chilli in HK...
So why am I still here in HK? Cos my hubby is from HK and he will not move to SG. But having said all that, HK is still a relatively easy place to live in, with easy access to transport, shopping, food...if you forget all the minuses I have just mention, one can still be relatively happy living here!