Only issue with the citibank amex is that it is amex and not accepted everywhere in Hong Kong and it gives you the cash back but you will not accumulate any points at all. The Manhattan platinum has a kind of scale but a normal expenditure of around 5000-20000 a month gives you 1% off everything (more than 20k gives you 2%) as well bearing in mind that it's a visa card and more usable. Not to mention the fact that you get your normal points as well which is effectively another 0.4% off or so.

http://www.manhattancard.com/reward-.../en/index.html