Would you mind to elaborate on your problems with Zabbix?

We use it for a small ISP since nearly two years and are quite happy with it. All limitations that came up during integration could be fixed by writing some small scripts. Even upgrades worked.. :)

So if you have any Zabbix pain that might be waiting for us, please share.

Can it be completely driven by some configuration management tool and run without persistent storage? These are two parts of nagios that make it work for me. Granted, I didn't look too far, but some basic research says you need a database and have to manage everything via GUI.

The data is stored inside a relational database, which might become a problem in the future.

They do offer an API that is quite usable. I've build a simplified interface for our less trained staff members with it.

You won't find any RRD files which might be a problem for you. Until now that was only a theoretical problem for us.

Yea, you are right. On the other hand, you usually define the templates once and then it kinda works automatically via discovery.