there is no comparison between Nagios and Zabbix. Zabbix wins hands
down. Having worked with Zabbix since 1.4 it has evolved into a great
product and the features coming into 2.x are amazing.
Some features that Zabbix has that Nagios is lacking:
- Auto Registration
- Auto Discovery (agent devices, snmp, etc..)
- Aggregate Graphs (this is very useful when looking at the overall picture)
- Distributed Monitoring
- Windows Service Discovery (coming in 2.x)
- Native JMX Support (coming in 2.x)
There are many other features that Nagios just doesn't have, not to mention the ease of use.