Nagios questions

[J. K. Cliburn]

So I've recently set up Nagios for the first time on a test server here 
at home.  We use Big Brother at work and I want to see how Nagios 
compares.  It's my understanding that in order to monitor parameters 
like, for example, disk and process status on remote machines, I need to 
install nsca or nrpe, which are Nagios add-ons that run on the remote 
machines.  Can someone on the list tell me which of these two are 
preferred above the other, and why?  Is it better to run the add-on 
under xinetd or standalone?  Also, do you prefer Nagios to Big Brother, 
and why?  Under what circumstances would you ripout a working instance 
Big Brother and replace it en masse with Nagios?

Thanks,
Jay