My experience with this is Centos is very stable, but I find Debian and Ubuntu are easier to update. The ability to quickly and easily run updates such as security patches for my software gives me peace of mind.
As a real world example, I had to setup a VPS to pass a PCI-DSS compliance scan. Using Ubuntu Karmic Koala with pin-holing for Aptitude packages, I setup the whole server and passed a few hours. By comparison, installing single PHP packages for Centos 5 when there is no yum packages available - and I had to compile my software and a lot of dependencies - has taken roughly the same amount of time for less work. This is the real difference for me.
I have had a server running Centos 4 and Cpanel compromised through brute force attacks. As gravyface has suggested though, this was probably more a configuration thing, and if you're prepared to spend a bit more time setting up Centos 5 then it is probably fine.