Traflying,
I'm a Singaporean who was based in the US for the past 2 years, and I'll say that UA miles are one of the best mileage currencies around. They are a part of Star Alliance, as is SQ, and can therefore be used to accrue miles from SQ flights (except for the SQ fares that only earn 50% or 10% on KF, which do not accrue on UA at all). UA miles don't expire (unless you have had 18 months of account inactivity), they can be used to redeem award tickets on multiple Star Alliance airlines on the UA website, and UA does not charge fuel surcharges UNLIKE SQ. I recently redeemed 70k UA miles on a one-way ORD-DUS-FRA-ICN-TPE-SIN on a mix of LH F, TG C and SQ C. Total price: US$52 for taxes and fees, US$25 for booking over the phone, and US$75 for changing the date, i.e. US$152 all in. SQ will never give you something this cheap even when flying SQ C or SQ F longhaul.