If you are starting fresh, using CentOS 7 with packages from the EPEL repository would be a good choice. EPEL provides many additional packages but has a policy of not overwriting or conflicting with the packages from the base distribution. For earlier versions of Centos you can only get current OCS packages from the Remi repository, but that also contains packages that will replace base system versions which can be dangereous if you run other applicatiions on the same system.