Well - it's much more personal choice. A bad configured MySQL won't run much faster - doesn't matter which OS one is using.
Personally - and that's just personal - I like the structure of BSD more than Linux where a GNU Kernel is used with userland tools every distributor may freely choose - the BSD base is much more one system where anything 3rd party is installed from the ports.
Just saying - bad configured services won't perform much better if OS xyz is used so best choice is to use what fits your needs - you know - Servers are the wrong machines for learning & playing & trying what command may cause what
Agree with your comments
At this moment I'm very satisfied with Debian, I get all that I need with a few commands and I'm very used with it.
Maybe the personal choice is like use any personal distro, the best distro will be that one that satisfies your requeriments.