Operating System CentoOS 6 (x86_64 bit) CentoOS 5 (x86_64 bit) Ubuntu 11.10 (x86_64bit) Ubuntu 10 (x86_64bit) Fedora 14 ((x86_64bit) Debian 6 (x86_64 bit) openSuSe 10.3 (x86_64bit) openSuSe 11 (x86_64bit)
If you are using a control panel below is what I recommend. cPanel - CentOS Plesk - Windows Other OS flavors can be used depending on the website structure and requirement.
The best Linux operating systems at the moment are CentoOS 6 (x86_64 bit) or CentoOS 5 (x86_64 bit). Ubuntu is also not bad, but it is easier to configure and operate the services on centos.
this is really just a personal preference and you should go with the one you're most comfortable with. anyhow, CentOS and Debian, IMO are mostly used for VPS'es, because they're easier to manage, are stable and supported with upgrades and security patches for many years.