Heya and welcome to MR.
I am in your neck of the woods these days - I have relocated to Hong Kong. Funny, those 3 ereaders you saw in HK might belong to HK members here on MR. lol
Generally, not a whole helluva lot of dedicated ereader devices in HK.
So, to your question.
Cannot speak about the Nooks. Have seen them and played with them of course in NYC, but never owned on. One thing to consider, besides the LCD/eink screens of the various BN devices is whether or not you will be able to take advantage of the BN ebook infrastructure in Singapore. Of course, this applies for Kindles as well to a degree.
I have a new K3 which I had visiting family bring to HK from the States. I chose the Wifi one because I don't need/can't use the 3G Amazon service here in HK. But even if I could, I am not sure I would. I have an enormous ebook library that I have collected over many years and I am perfectly content to use awesome apps like calibre to convert my stuff to K3 friend formats and then sync via USB. But even though I am physically in HK now, I can still take advantage of Amazon's great free auto conversioon email service - I send them books in one format and they send them back fully converted and K3 ready. I simply add to calibre and then sync to Kindle. Done.
Again, speaking only about the K3: in my hands it is quite a delight to hold. Very light, dimensionally very good and extremely thin, even with the book type cover I have. Build quality is only OK IMO -a lot of stories about K3 being relatively easy to damage, but Kindle Customer Service is doing an exceptional job offering free replacements in most cases. K3 has 5-6 font sizes so ease of reading should not be an issue.
Of course, I would like the K3 to have a touch screen or perhaps to get rid of the keypad [zero utility for me really] and up the overall build quality. Still, for the money I continue to think the K3 is a great purchase - it does basically one thing and does it very very well. The eink Pearl screen is excellent in nearly all lighted conditions, but of course, for night reading you will need a lamp or an attached book light.
Tons and tons of accessories for Kindles out there.
The newest NOOK seems quite a good device as well, basically IMO a K3 with a touch screen. Have not seen one in person yet so no idea about build quality, nav, etc.
Tons of really knowledgeable folks here on MR that will give you far better advice than I can.
FWIW, I hope the above helps...cheers!
-les