I'm taking it to the web to vent a bit accumulated frustrations with setting up a server configuration on CentOS. As a Debian user (and fan, I might add) I appreciate a distro that is up to speed. No, I'm not talking about cutting edge, but a distro that is able to offer the ability to keep up with developments in a timely manner without sacrificing stability.
CentOS is nowhere close to that and I believe that the market share statistics from W3Techs show it. The yearly graph shows what I mean.
Debian has surpassed CentOS in early 2012, while Ubuntu has overtaken CentOS as well in early 2014.
And for good reason. The CentOS policy seems to be to use the oldest supported version, even in the case of important software such as the kernel (as well as server-side technologies like PHP).
Against all reason, CentOS has held tightly to the 2.6 kernel since 2011 until late in 2014 (version 7 has brought kernel 3.10 instead of 2.6, which isn't even a performer among the 3.x versions - that would be 3.12). The kernel also matters, as it has a lot to do with disk access, memory management and access to other hardware resources. A kernel alone can improve disk IO, memory access and whatnot, resulting in very slight improvements across the board for web servers, caches, db servers, etc. Many very small improvements that tend to add up for servers under stress.
PHP is another offender, with CentOS leaving PHP 5.3 in the dust exactly at the time it reached end-of-life before moving to 5.4.
Slow to update and without offering 'cauldron'-type repositories, CentOS's worst sin is that it doesn't allow any easy means to prepare your systems for the future.
Debian offers 'unstable' and 'testing' repositories with clear procedures in place. For example, when the 'testing' version reaches its freeze, I can pickup a server, plug 'testing' in and check my applications against upcoming updates in minutes.
On CentOS my only choice is to manually compile packages. It's not the worst thing, but between my desired configuration and its dependencies I might as well build my own flavor of Linux (some people do that). It's no wonder that CentOS/RHEL have lost to Debian/Ubuntu (as of today, 58.4% market share against 24.9%). As a sysadmin, you get to roll with the flow incrementally on stable. Keeping with the same PHP version which is 9(!!!) years old doesn't bode well.
Will Ubuntu overtake Debian? It's possible. I like Debian because it's very light on server resources when compared to Ubuntu. Then again, when you add up services, for similar configurations you'll reach the same hardware requirements, with the distinction that with Debian you will get to add software while with Ubuntu it's likely you'll look at removing packages. Today hardware resources are getting cheaper so Ubuntu is both famous and affordable nowadays yet Debian has a clear advantages for developers using tiny VPSs while allowing a seamless future transition to Ubuntu.