What NMS do you use and why?

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.