Stock 4.4.4, Franco kernel r57, TWRP 18.104.22.168., that's all.
I played around with different ROMs and such on my previous Nexus phones (NS4G and GNex), but I've come back to stock Android. I don't really care for all the customization that ROMs offer, I never used most of them anyways. I've found that I prefer the relative stability and minimalism of the stock OS, plus being able to use official OTAs and Factory Images is nice. Of course, low-level customization is a different matter entirely, so I use Franco kernel to tweak CPU performance and efficiency.
I'm an avid overclocker, so as long as I can control CPU frequencies and voltages, I'm happy.