Which one is preffered ?

I recently set up a Nagios installation, but it had to be hacked to run on my servers. It is also debatably unsafe as it apparently (I cant confirm as I have never felt the need to hack my own servers) leaves backdoors open.
Thats just what I've heard.
~Equinox

If you've got the time, I would recommend Zabbix. Nagios is also good although a bit annoying to install. Once configured though, it is pretty darn accurate.

Roj

NetStatus is no longer developed to my knowledge. Nagios hands down.