UA puts China and Singapore into two different regions, and a SIN-China award needs 40k; while AC puts China and Singapore into the same region, and a SIN-China award need only 20k miles...

That said, UA is better if you fly 50k miles or more in a year, because they give 100% bonus miles when flying United metal, and more importantly, their economy plus seats...

info is just a few clicks from the AC website...

- it's not that surprising that it takes 20k miles. 20K NW (Northwest Airlines) miles also get you SIN to anywhere in China roundtrip on CZ (China Southern). 25k DL (Delta) miles get you SIN-PEK/PVG/CAN roundtrip on SQ.

- take into consideration the YQ (fuel) and booking surcharge you may get hit for award tickets. E.g., SQ charges YQ on award tickets (i believe it's more than S$100); NW doesn't charge YQ, but when you check in at SIN CZ will charge you YQ; DL has extra booking fees for award tickets. AC charges YQ on award tickets originating in north America and europe, but not those within Asia at this moment.

- another nice thing about AC/NW awards is that you can go to anywhere in China. This comes handy when you are flying to small a city/airport, to which there's no discount for revenue tickets. It saves you a lot. 20k UA gets you a roundtrip ticket within China, which also not bad. I once got a ticket CAN-PEK-DDG-PEK-CAN on CA for 20k UA miles. If I were to buy it, just the PEK-DDG-PEK portion will cost almost 2k RMB.

- yet another benefit of award tickets is that you can get free "stopovers". Technically speaking these are not stopovers but connections of less than 24 hours. E.g., we once had SIN - BKK (stop for 20 hours) - PVG (main destination) - HKG (stop for 15 hours) - SIN for 20k AC miles. We had one whole day in BKK and almost one whole day in HKG for free. :)

enjoy flying...