I recently redeemed an award ticket on SQ using my UA miles for CGK - JNB for next year World Cup. It was 70,000 UA miles plus $36.80 in taxes. I logged in to KrisFlyer and the same award would have cost 46,750 miles (inc. 15% disc. on online redemption) + $39.80 airport/government tax + $254.00 Fuel Surcharges (YQ)

While mileage requirement for redemption is significantly lower on KrisFlyer, the high tax and YQ pretty much offset the mileage difference.

I guess it all depends on what value you put on your miles. In my situation; at 1 cent/mile, using UA miles is cheaper. At 1.5 cents/mile, KrisFlyer is cheaper. They are about equal at 1.1 cents/mile.