Just since I recently had both on my desk - when they both are idle then the SQ is quieter since it slows the internal fan.Better is the PWS-920P-SQ or if you are not going to drawless power then the PWS-501P-1R (no personal experience on the 501 - just read its about the quietest SM psu you can get for this chassis.
When running normally/fans present they are equally loud (or silent) - therefore I tend to use the 501P due to increased efficiency.
On a side node - the PWS-1K03A-1R (Titanium) is also surprisingly silent and should handle low power builds well due to increased efficiency