Cpanel is most popular control panel for Linux servers.

I used to support many distros. Recently they changed policy to only support CentOS and RHEL Linx distros. They also support FreeBSD, but recommended only for expert users.

http://www.cpanel.net/products/cpwhm/cpanel11/sys_requirements.htm

It is a good move as it make them easy to prodie support and make cpanel work better on these supported OS. Both CentOS and RHEL are same.

I used to have 2 FreeBSD servers with Cpanel. Many says FreeBSD have better performance. But i don’t really see any difference. I swicthed most of my servers on Linux as it is easy to get support than on FreeBSD when you have a problem. With FreeBSD + Cpanel, you will have to find solution your self as most use Linux with cpanel.