I've always liked Noctua fans (own quite a few of their various old school brown verities), and their A12x25 series are impressive in the performance/noise balance. However, the new black version is $35 + $4 shipping.
But at double the price as a fan like the Be Quiet Silent Wings 3 PWM fans (which are my current favorite fan series), these new fans are a very tough sell for me.
One of the biggest things that I'd like to see is a system like Lian-Li uses where you can slot fans together for easy power relay. Although, you'd have to hope that the radiator that you use them on respects proper fan spacing, or it wouldn't work.
I was going to use Arctic fans with my build simply because they're far cheaper (~$10) and... while not as good performance, they're fine for radiator fans. I got their PST models, but I just didn't care for the method of daisy chaining the fans. The male connector that facilitates the daisy chaining wasn't really long enough, so it caused me to have to essentially reduce the cable length, and I ended up having to use an extension to even reach the fan controller. In the end, I bought a bunch of these Noctua fans to use on two builds.
$39... for a case fan? You must be joking!
The non-Chromax version of the NF-A12x25 is about $30 too. I mean... even if you go with the fairly spartan version that Noctua puts out, the fans are still around $15-20. One thing that I do like about the NF-A12x25 is that they come with rubber gaskets that you use in between the radiator and fan to help reduce air leakage around the fan's frame.
Awkwardly, one issue is that if you wanted the absolute best performance, Noctua fans offered the best cooling in regard to noise levels. Although, ever since Phanteks released their
PH-F120T30 30mm thick fan, Noctua has some strong competition. Although, the fans are 5mm thicker and also pretty much out of stock everywhere.