There are a lot of good fans here and considering the human ear is only capable of sensing 3dB rises as "Barely Perceptible", I would consider that a good indication of why fan preferences are so varied. They all have similar noise characteristics. I think I have collected a good group of performance numbers, particularly the CFM vs Volts chart, I would use that to give you a sense of fan power.Subjective Notes
I don't necessarily think there is a means to accurately identify which fans are necessarily better than others that would be agreeable to all. There is far too much personal preference that determines which tone or characteristic sound and power requirement is desirable. With that said I see several generalities:Motor noise is generally smoother the smaller the fan motor hub, but also a higher pitch. 38mm fans with the extra large fan hub general have more of a pulsing or motor ticking type of sound when running very low rpm levels. This measures low from a dB standpoint, but it's a noise that many may not like...you really need to listen to the videos to see that.
Noise tone and quality often times varies across the voltage range, sometimes it can even get worse at one voltage and get better with a higher voltage, it's one of those sound dynamics that occurs.
Fan generally produce more CFM per RPM the thicker the are, the more curved the blade, and the more number of blades.
There is no consistency between fan families. I've seen several cases where the same series of fan has very different sound responses; you simply can't depend on consistency there.
It gets really hard to choose between fans in the silent 1000 rpm or less category. My instruments were simply not able to measure CFM levels that low and to my ears, they are all silent down at that level.
As much as I've tried to quantify things as scientifically as I'm able to with the equipment I have, I would emphasize that you listen to the videos as the primary means to compare fans and make your own personal preference choice. A really handy way to do that is to start up two window browsers with a video in each window, then use the sliders to match up similar CFM levels and pause each movie. Then go back and forth between each fan and see which one you like the sound tone of better. I think this is different for everyone, and you should make your own decision on what you like...not what I or anyone else likes. You can also use the charts to understand things like how powerful the fans are, what RPM range they can produce, power requirements, etc....but I'd use the video as the main tool here.
If I had to pick just one fan for my needs. I want something very quiet, but something that also has a decent amount of performance. While being a bit on the ugly side, the Gentle Typhoon AP-15 gets my top pick for producing the most CFM per noise level and quality of the fans tested. 9 volts in particular is my favourite spot which is still producing a good 22+ cfm on the radiator.
For the high speed stuff, I'll give my kudos out to the San Ace. I still think it has that common 38mm fan motor noise when undervolted, but it's the smoothest of the bunch from what I can tell.
As far as the <1000 rpm range, i think all of the fans (except high speed 38mm fans) are good and really hard to separate. couldn't measure cfm below 10cfm, so tell you much with my test setup other than is pretty crappy down there better plan on many times more radiator someone strong fans.
King of Power @12V = Delta AFBSHE
King of Low Noise @ 12V = Noiseblocker S1
King of CFM per Noise Level/Quality = Gentle Typhoon AP-15
I wanted to give a HUGE thanks to www.petratechshop.com, www.ncix.com, www.feser-one.com and XS member HondaCity. Also KaptCrunch for helping me out with the sound meter. This test would not have happened without their generosity.
For reference you can check out Madshrimps 35x 120mm Fan Roundup