Re: best 120mm quiet fan
For a CPU cooler I'd say an S-Flex. They have plenty of pressure which make good CPU coolers, where as the Noctua and Yate Loons are great case fans as they're quieter and push a decent amount of air. You don't need a lot of pressure for case fans since you'll be using more than 1/2 if you have a good case.
Edit: I have 7 Yate Loon low speeds and they're silent. Maybe the High Speed models sound loud, but I wouldn't even touch those as these low speed ones do the job perfectly.