What NMS do you use and why?

[Colton Conor <colton.conor () gmail com>]

We are looking for a new network monitoring system. Since there are so many
operators on this list, I would like to know which NMS do you use and why?
Is there one that you really like, and others that you hate?

For free options (opensouce), LibreNMS and NetXMS come highly recommended
by many wireless ISPs on low budgets. However, I am not sure the commercial
options available nor their price points.