In a base 10-12 SEER models, the slope top Tempstar probably win the award with ratings on low fan as low as 68 db. When you get 13-15 SEER then the nice Lennox units and the high end York products can get as quiet. Some of the Carrier Silencer system units too.
Really need to listen to a unit if sound is that critical. db ratings alone don't tell it as Q sez.