Hi, I've used NF-R8 fans and while they were fine there wasn't anything 'special' about them from my point of view. I don't know how the NF-B9 is. I have used Arctic Cooling F9 fans in 3pin and 4pin PWM formats and really like them. They seem very smooth and quiet, they have some sort of 'fluid bearings', long warranty and low price.
+1 (I own the R8, the B9 and F9): IMO the B9 aren't the best fan around, while I would also recommend Nexus 92mm (NOT the transparent PWM ones).
But priorly check which type of fan header your mobo has, as maybe you'd better to pick a fan controller.