Singapore recently devalued its frequent flyer program, KrisFlyer, but it also got rid
of exorbitant fuel surcharges, which evened things out in the end.
United typically does not charge
exorbitant fuel surcharges or other hidden fees for its own flights or flights on its partners like you'll see when redeeming Avios or American Airlines miles on British Airways.
Air Canada, Air China, Air New Zealand, Turkish Airlines, and United Airlines do not pass on
exorbitant fuel surcharges to award tickets, so I recommend booking flights operated by those airlines if possible.
As always, be careful and do not book your flight on British Airways unless you don't mind paying
their exorbitant fuel surcharges.
Other European airlines have
exorbitant fuel surcharges.