I've lived in Singapore for seven years and just returned from my 4th visit to Bali, and would wholeheartedly recommend Bali, especially staying at a good resort in Ubud -- eg. the Komaneka Bisma is amazing.

I like SIN, but it's just not all that different from HKG. Trying to squeeze SIN and another city into three days will just mean that you spend half the trip in airports. Tioman is not a realistic option, as March is still the monsoon season on East Coast Malaysia and most resorts, ferries etc will be shut down.