Hi,
there's many different options to use on a test, for alternative dedicated distros take a look at
BlackBuntu or
BackBox for example.
Additionally you don't need to use a dedicated pentest distro to perform pentest activities. My main machine is a vanilla Ubuntu (Mint) installation with my preferred tools either installed from repos or compiled from source. Plus I keep a BT VM image handy incase I need to rapidly confirm output from my own system, or access a tool a rarely use.
The main reason for using BackTrack, especially in a training environment is that it ensures that all student system configurations (should) be identical, so effort can be focused on learning the tools and techniques, rather than trying to troubleshoot each student's unique configuration issues.
Ultimately use whatever you feel comfortable, try a few and see what works for you.