I want to know which operating system will be more stable for a cpanel
cPanel does not support Ubuntu, so you can rule that out. I would recommend installing CentOS6 and then upgrading it to CloudLinux (which is based on CentOS). CloudLinux lets you protect your server against abuse. CloudLinux is a great solution for shared hosting providers.
If your VPS is running under OpenVZ, you cannot use CloudLinux, so stick with CentOS6 in that case. Here is a link about CloudLinux not working under OpenVZ: http://www.cloudlinux.com/vz-compat.php
cloud linux if
1) You use VPS for shared hosting.
2) You can spend few more bucks as cloudlinux is paid.
just go for CentOS6
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