I signed up with these guys about 4 months back after having used CSD and then manage workplace NOC.
I think ITimpulse provides the best NOC services. be it response time, resolution time , cost or ease to reach them, i have never been let down. I have been able to build costs for NOC in my service offering and have reached about 40% (of revenue) MRR with 70% profit margins. Thats industry best.

I would highly recommend ITimpulse NOC for not only the NOC but a host of serviced they provide for MSPs like me.