You're right, one does need to be pretty careful when buying "quiet" fans. Most of them are cheaply made and overhyped. Also, the methods used to rate fans varies tremendously. I'm not sure where Akasa gets off rating a 1400RPM fan at 18dBA, but a rating like that is simply dishonest. A noise floor that low is physically impossible if you're measuring it "normally." The plastic housing also looks light and low-density, which causes more vibration and rattle.
The Nexus quiet fans are made by Yate Loon, and they're a pretty reputable company. I'd go with the Nexus, which are basically the same as these:
http://www.case-mod.com/store/120mm-case-fan-yate-loon-d12sl12-orange-quiet-fan-p-1709.html
I have about seven of these fans and they're of exceptional quality.
Buying fans based on specs isn't the best way to go about it. One can generally rely on the bearing type, RPM, and pressure specs to be accurate, but after that it's a crap shoot. Your best bet is to stick with a list of reputable manufacturers. I'd trust just about any fan from Delta, Sanyo Denki, Panasonic (Panaflo), and Yate Loon - their products are consistently of high quality.
Reviews also tend to be a load of crap unless they're from SPCR. SPCR is a pretty solid resource for this kind of thing, but be warned that you can spend WAY too much time there.
They know their stuff.
*Edit* One more thing. Don't buy fans from companies that don't make fans. Akasa, Thermaltake, Scythe, etc...none of these guys are real fan suppliers. In fact, I think the only Thermaltake really makes is gobs of transparent colored plastic, and they probably outsource for all of that, too. These companies just buy fans from someone else, relabel them, and mark up the price.
The normal speed sounds like 28dba
Sounds like 28dBA? Also, the fan in your Seasonic is a Yate Loon, if I remember correctly.
