GENTOO allows us to customize everything and to build it the way we want, such as the build flags, compile time flags.
GENTOO is also used by google for their chromebook
GENTOO usually has packages for latest packages, that is if new version of anything comes out, the script that allows compiling is usually there in a few days
GENTOO allowed us to integrate vserver technology properly,
for serverware that is
GENTOO with pbxware was chosen as we could, as I said, choose our own compile-time flags deciding what goes in and what goes out
There is also no version for GENTOO, that is something others are jumping to as well, it is basically just releases.
We do not use CENTOS because CENTOS seems like an abandoned project,
it is based on rhel5 which is built like 2006, so the core libraries/kernel is basically from that year 2006-2007.
CENTOS is fixed so if you want to run some new software
the latest and greatest that relies on stuff from later period
There is no CentOS 6 yet.
REDHAT rhel is closed which brings up royalty issues, it is forked in almost all cases with their own patches
REDHAT patches for everything and their kernel is different
and everything else is different to stock version
RHEL 6 looks good, but as I just said, it is REDHAT-way and no other way