I've found FreeBSD (4x) the easiest UNIX derivative to install, the kernel is easy to reconfigure and apps are easy to install.
The sh*t hits the fan when things don't work as intended, but that's the same with every UNIX derivative. You've got to be an expert if (and it's not uncommon) stuff goes wrong.
The partition managers in every UNIX derivative's installer I've found to be the worst of any operating system. They allow stupid things like totally invalid partition tables to be set. My experience of UNIX derivatives consists of quite a few Linux distros of varying versions, and FreeBSD.