I'd say you lucked out with your Quiet One. I had one on my 75 and I found it noisy. It also did not restart sometimes after a power interuption. They do have a nice watts to flow ratio, though.
I've heard that the Velocity pumps are really quiet, but they add more heat than most other pumps. This may not be an issue on a 180 sized tank. The T4 model pumps 1275 gph at zero head. They are external.
I'm looking for a pump for my 180, too, and I'm also trying to keep things as quiet as possible, as well as efficient. My plan is to get the circulation I need in-tank from stream type powerheads. I'm just looking to have enough sump flow to feed a skimmer and fuge. I'm hoping this will reduce watts and heat added as well the noise level by reducing the amount of water going through the overflows and spilling into the sump. I'm looking at an Eheim or maybe the Tunze recirculating pump.