If you put five Linux geeks together in a room, you'll get five different opinions and no agreement on anything. With that said ...
Nothing makes any OS better then any other. It's all a matter of (i) outlining your goals or objectives; (ii) identifying the relative strengths and weaknesses of the various OSes out there; and (iii) selecting the OS whose strengths match most of your goals or objectives. Even then, you'll find yourself, most of the time, having to pick from more than one OS (a testament to the quality of most Linux distro's out there). Thus, often, the most cited reason people give as to why they chose one distro over another is (iv) personal preference.
At their core, Ubuntu and CentOS are EXACTLY the same: Both are built on the Linux kernel.
Normally, distributions are made for specific reasons and have been tailored to address a series of concerns. There are many versions of Linux that were developed specifically to be installed on servers that receive heavy traffic, like web servers. Some distributions of Linux were developed to be used in networks where security is a priority; where sensitive information should only be accessed by a privileged few.
The basic differences between CentOS and Ubuntu are:
CentOS is based off of RedHat and Ubuntu is based off of Debian. For serious - near enterprise - level server requirements, CentOS would suit you perfectly. The downside (for some), however, is that RedHat has a tradition of being more conservative (not so quick to provide the 'latest and greatest'); thus, CentOS is also 'conservative'. In contrast, the package repositories of Ubuntu contain fresher packages, while CentOS tends to focus more on security patches. Many regard Ubuntu as a good, easy to use OS and, thus, a perfect starter server for those who are willing to learn Linux and don't know where to start.
I anticipate that the most influential factor for most newbies are the "communities" for each respective distro. If you are looking for which is better for you, I would suggest to browse through their forums and see which one you like better. I would venture to guess that the Ubuntu forums will have more newbies than the CentOS forums--hence, you'll probably find answers to your questions a lot quicker/easier, simply b/c you'll share a lot of common questions with more people in the Ubuntu forums.
If you're married to cPanel, then you have to run CentOS--cPanel doesn't work on Ubuntu. If you're open to an open-source control panel, such as Webmin/ Virtualmin; ISPConfig 3 or Zpanel (or, better yet, no control panel at all!), then either distro is fine.
In 2012, W3Techs
reported that Debian became the most popular web server in the world. The report went on to note that many sites subsequently switch from Debian to the Ubuntu distribution (which is based on Debian). One note of caution, however, is that Debian had held the No. 1 spot before and it lost that position in June 2010 to CentOS. So, it's fair to infer that people's preferences change quickly.
Bottom line ... either CentOS or Ubuntu can/ will do. They are very similar and after someone becomes comfortable with one, the other distro is not that difficult to dive into (you just have to remember where things are located).
According to DistroWatch's Page Hit Rankings
, the most popular Linux distributions (for the last 12 months) are: