Quick question: Choice of release

["Anders Breindahl" <a.breindahl@post.cybercity.dk>]

I and a friend are playing with the idea of convincing our gymnasium to 
using Debian GNU/Linux as their main server OS. 
 
As it comes to this issue, which release we would want; stable, testing or 
unstable? 
 
Making the choice, it would matter that the focus is on reliability. We 
would want it to be absolutely reliable and secure. No security flaws would 
be accepted. On the other hand, we wouldn't want it to be outdated, so any 
performance-fixes are not included. What is the best compromise? 
 
Regards, skrewz a.k.a. Anders Breindahl.