Debian is really well-made, we've used it at my college to host a yearly programming competition since 2012, it's stable, quick, and rather simple to maintain, especially if you're not doing anything too complex, other than hosting a couple of PHP files on top of a web server, that's the full scope of what we've done. I am not a security expert so that I couldn't answer on, we've not yet had any breaches yet, despite all the major things that came out last year or so, 'Heartbleed', and 'Shell Shock'. I think the best option for you is to try it out on one machine maybe via LiveCD and see how you like or don't like it.