Having only visited Singapore I can only make the following observations:
Regarding the 'fun for singles' debate I can confirm that it is possible to get laid in either city.
Regarding the 'wonderful street food', this is the biggest myth about Singapore. I was looking forward to having great street food in Singapore but in reality the hawker centres are little different from 'Food Courts' in shopping malls in Hong Kong, the same food, same signage same stuff everywhere. In fact, despite the HK government's anti-hawker legislation and education, designed to limit hawking in favour of their mates in big business who own restaurant chains, Hong Kong still has better street food than Singapore.
Thanks for excellent comments for everybody ! I have made my decision to move to Hong Kong. My plan is live there for next couple of years at least. I will arrive ther 1st October, so see you around there..:-)
if your aim is to make $$$ - i will choose hk.
if you a family man with kids - i will choose sg.
if u a single or party animals - i will still choose sg :-)
i live in both sg and hk for many years... i experienced life style in both places.