When new, Noctua fans are excellent. However, whether they stay quiet is another matter. Their 'noise reliability' is very poor, all the ones I've had developed a relatively quiet, but annoying high pitched whine after a couple of weeks, something SilentPCReview criticised them for.
I care a great deal about quietness, and thus pick the smoothest and least irritating system before I go by decibel count. In this case, this is Scythe.