[CentOS] Migrating away from Nagios

I have to rebuild a new Nagios box and thought this might be a good time
to migrate away. I use snmp mostly for everything but with the fork Nagios
endured I wonder about putting any more effort into the project.

I probably should look at OpenNMS again, but the other options I think might
work are Icinga (Should be trivial to migrate) or Zenoss or maybe even Zabbix?

Anyone have experience in Nagios and care to share comparisons with similar
projects with strong community involvement?

Also, anyone currently running OpenNMS that can comment on the learning curve
and level of flexibility coming from a Nagios user?

Thanks!
jlc