I was originally thinking about getting the Noctua, but then after seeing the Phanteks, I'm not sure. The resaon that I was looking at the Phanteks was because it has two 140mm fans instead of the 140mm and 120mm the Noctua has. However, can you install a 140mm fan in place of the 120mm on the Noctua?
I had the same question; I ended up going for the Phanteks for several reasons:
When using good fans (the stock ones aregood, but sound like jet engines), it performs several degrees C better than the Noctua.
Color options; I got a solid black Phanteks to match my other components and case, and it looks great!
140mm fans - both can mount them, but the Noctua can mount 120s, as well. The Phanteks, out-of-the-box, can not.
I would get a Phanteks, if I were you. It performs better, can look better, and doesn't have brown fans.
The Phanteks fans arent the worst, i have some and there a little loud for me, mainly the hum, but even at 12v in the front of my define R4 they run moderately well, so you could get the Phanteks and run the fans on the equivalent of 7v, but the NH-D14 will come with fans that are already pretty damn quiet and probably cool just as well.
Edit: just found out Phanteks has revised there fans for 2013 making some changes to the way the MVB works, so it may be quieter than what i have or anyone with one has experienced.
Noctua D14 is a great performer that is extremely silent. I would go for that one, besides Noctua has an amazing reputation, always nice to know if an issue comes up.