FreeBSD 6.0 is better than CentOS but I believe CentOS has better support for cPanel. If you'd like to go with FreeBSD (and you should! ) then you can go with the DirectAdmin control panel which works perfectly with FreeBSD and isn't bloated like cPanel.
If you're talking about cPanel servers, then CentOS has much better support. In fact, cPanel does not even officially support FreeBSD 6. It is neglected as a platform.
Now if you leave cPanel out of the picture, then we usually prefer FreeBSD for its own merits. In our experience, FreeBSD has always been more reliable and easier to maintain than most Linux distributions. If you don't need a control panel, or if DirectAdmin or Webmin will work for you, then you might consider using FreeBSD instead of CentOS.