Its hard to compare CentOS with FreeBSD, since they "do things" very differently, even though they are both *nix-based operating systems.
CentOS, as everyone knows, is the Fedora/RedHat result for the corporate RHEL (RedHat Enterprise Linux). Its a stable operating system with a lot of support, but if you want to compare it with FreeBSD then you have to ignore the application layer (apache, cpanel, whatever) and look at the true operating system details and differences.
In other words, you compare the Linux Kernel with the FreeBSD Kernel. At that level we see the following:
1) Linux has a lot more "general hardware" support, while FreeBSD is targeted towards hardware related to networking.
2) Linux has a mature SMP support, while FreeBSD has just gone SMP in the past 4-5 years. In practice that means that some drivers and applications in FreeBSD don't take the full advantage of SMP (which is not a problem in FreeBSD v6 and onwards).
3) Linux has a lot more applications natively made for it and a lot more support and user base than FreeBSD. While FreeBSD has a Linux emulation layer and can pretty much run everything.
4) Now the tide turns, since FreeBSD has a far superior TCP/IP stack with a much more advanced secure layer embedded in the kernel than Linux (remember FreeBSD's relation with the most secure os, NetBSD). As a result, in pure numbers, FreeBSD has the fasted processing of bandwidth ever.
5) FreeBSD's memory management is far superior to that in Linux. When dealing with large number of processes and threads (Linux is very bad at threads) it does it fast, efficient and with as little swapping as possible.
6) FreeBSD runs natively a jail system that practically stops all attacks for root access, while the Linux equivalent is not a complete jail (apache/php and friends all run as system processes, while in FreeBSD everything can be jailed). Even if you get root, you'll be root in a jail.
7) Overall, Linux is more "bloated" compared to the lean FreeBSD. No extra modules and no extra RPM dependencies.
So what am i talking about all this time? Comparing Linux with FreeBSD by looking at cpanel or apache or another application is really completely irrelevant, instead you should look at the services each operating system provides.
Personally, i run both CentOS and FreeBSD as servers (i use Fedora for desktop), Linux is friendly (as friendly as a unix system can be) but FreeBSD is a more stable, leaner, and a more reliable server.
So what should you choose? Since this is about a hosting service, it doesn't really matter, anything you choose to use will work fine, unless you need some kind of extreme server with several million requests per minute, then go for FreeBSD, otherwise it shouldn't make any difference.