I have a Nanoxia DS5 filled with NF-14's. There are quieter fans, but these actually stay quiet for more than a year, I replaced the H110i GT fans with the Noctua's as soon as I installed it, massive difference in sound even if it is moving a little less air, and my CPU stays below 47C at a heavy overclock running Prime95.
The two Nanoxia fans that came with the case though are, so far at least, super quiet. They're moving even less air, but damn near silent. I'm keeping them in to see how they do over the long term, if they stay this quiet I'll probably trade out all of them for more Nanoxia fans.