I like Debian, but I think most of the web hosting world uses CentOS (or RHEL). If you use what most everyone else uses, you can benefit from other people using the same OS. It may be hard to find help for web hosting issues if you use Debian, since most people do not use it.
I'd probably avoid Ubuntu in a server environment, Ubuntu is more of a desktop operating system. I suppose it can be used in a server environment, but you'd probably be just as well off using Debian in that situation. Ubuntu is based on Debian.