Comparing price/mile for DBS: $18,000 for 100k miles
vs US Airways miles: 50k miles = US$1750 = HK$13,912 (using exchange rate of 7.95 for credit card payment). From time to time, US Airways will have promo like buy 50k free 50k (with the cap at 50k). So effectively, you will be paying the above amount and get 100k miles. Roughly 22% discount from the DBS price but the downside is you can get at most 100k miles at this price. Of course, it's not an apple to apple comparison since you cannot use US Airways miles to reedem CX flights.
vs SPG: maximum only 20k miles to be converted to 25k AM a year = US$700. From time to time, SPG also offers 20% off, so, the effective cost for 25k miles = US$560 = HK$4,452. This will turns out to be about the same with the DBS price.
vs Stan Chart Rewards 360 - you cannot just top up the pts whenever you want. And even if you have let's say 10k pts. You cannot buy 140k pts to reedem 150k pts equivalent to 10k miles. Correct me if I am wrong.
So, at this moment, the DBS offer is quite attractive to me if I need the pts.