The main reason for the move would be career progression, exposure to greater China and leading a bigger team. Basically if I stay in SG, it could be at least a few more years before a similar opportunity may open up. However this is also offset by my wife having to give up her career or at the very least putting it on hold, so there is a trade off.
Thanks for the inputs on pollution and schooling. Air quality opinions seems to be mixed. Some folks believe it is really bad while locals or expats who have been there a while don't seem to mind it. We did make a few trips recently to HK as a family, the kids and wifey loved the food but hated the crowds. One thing though, my wife seems to always fall sick every time she is here (she is asthmatic) so not sure if it is a coincidence since we are here for no more than a week each time. I do fly over to HK quite often for work as well but it is a whole different set of considerations now with the family.