No way are ATM rates better than money changers. Anyway, more on that later...

Rule #1: All ATMs charge the same amount for foreign currency withdrawals. So no matter which one you use, your card/bank will be billed the exact same amount to the penny. The only exemption to this rule is if you use the same bank for instance, like popping in your foreign Citi card into a local Citi ATM.

Rule #2: Banks and ATMs will always have terrible rates compared to local money changers. Best place to change are the Arcade money changers at Raffles Place where you are basically looking at no more than 1% off the mid-rate. Very often I was able to get virtually the same rate as the mid-rate listed on xe.com even, which was a surprise.

Rule #3: Consider if the amount you're changing is worth hassling over. I mean if you just want to change a grand then maybe it's not worth heading over to a money changer and spending time (+ money) to get there to save <$50.