I am looking to hear from people what they suggest is the best OS (*nix or *bsd based) for HLDS (Half-Life Dedicated Server) and SRCDS (Source Dedicated Server). Also please specify if you made any kernel modifications as well as what they were to improve servers fps rates (is there anyway to make it hold FPS?)

Thanks in advance.

Usually no stress with custom kernel in centos

CentOS is probably the best out of the box (with a few minor tweaks to the kernel). FreeBSD is great too but theres way more modifications you would have to do

CentOS is the best one!