Monitoring system recommendation

[Manuel Marín <mmg () transtelco net>]

Dear Nanog community

We are currently planning to upgrade our monitoring system (Opsview) due to
scalability issues and I was wondering what do you recommend for monitoring
5000 hosts and 35000 services. We would like to use a monitoring system
that is compatible with the nagios plugin format, however we are not sure
if systems like Icinga/Shinken/Op5 are the way to go.

Is someone using systems like Op5 or Icinga2 for monitoring > 5000 hosts?
Would you recommend commercial systems like Sevone, Zabbix, etc instead of
open source ones?

Your input is really appreciated it

Thank you and have a great day

Regards