I was looking for a NS assault rifle since I have characters in every faction, but after playing with the Yumi and the NS-11A i went for the 11A: equipped with a laser sight it has a very small hip CoF so you can use it in dire straits and it is a wonderful long-firing platform as well (high velocity, good RoF, stable) About the Yumi, I hated the small delay between the 5x bursts - a single burst is not enough to kill.
I like it, but you need to be stealthy. It's something of an assassination weapon, although it can hit running targets if they're not trying to dodge too much. At close range it can absolutely OHK, which is potent.