Recently it was published by DistroWatch that the Linux Mint distribution has passed Ubuntu and is now considered the most popular. In order from most popular on down, this list at DistroWatch starts with Linux Mint, followed by Ubuntu, Fedora, Debian, and openSUSE. There are others listed as well.
But I wanted to take a moment and touch on Fedora and the Red Hat based distributions to distinguish the differences among them. I am a huge fan of the Red Hat based distributions. Why? Well, I've used them since the early days of Linux distributions, and have been hooked ever since. I've had excellent luck with Red Hat, I like the tools that Red Hat develops and places in their distributions, and there is a huge support community for it. I've also found that Red Hat is a good company, and stands behind its products. It has been VERY supportive and active in the open source community for decades, and continues to show its commitment to open source software. I also think their software models are highly successful, with the Fedora / Red Hat split that we saw in 2003. Back then I was surprised with the split at first, but after a couple of years using both Fedora and Red Hat Linux, I soon discovered that the move to split the two was ingenious. I will explain why below.
So what is the difference between them?
Let's start with Fedora, which is Red Hat's free version. Fedora is sponsored by Red Hat and Red Hat developers, and is a cutting edge distribution. This means, that the very latest version of the kernel, and all software, is included. While getting the latest version of all of this software sounds appealing, it can also introduce some bugs and other problems that need to be ironed out. But, even with this said, since Fedora has such a huge user base and well backed development, bugs are usually fixed quickly and I consider the distribution very stable. I like the fact that I'm getting the latest and greatest software, because that means that I can easily get the latest version of Firefox, Thunderbird, OpenOffice (LibreOffice), and all other software included with the distribution. What Fedora lacks, is proprietary software. And this is because Red Hat tries to adhere to the original ideas of free software, which disregards proprietary products. Red Hat therefore does not release proprietary software within its distributions, which includes Fedora of course. This is why you sometimes hear of complaints about some proprietary drivers not working, etc. But, other developers have picked up the slack and an additional repository called RPMFusion contains proprietary software that can be added to Fedora. Since it is a repository, RPMFusion can be enabled on any Fedora system and then the Yum updater will see software from it and allow updates and software to be installed with ease. Support for Fedora can be found on FedoraForum.org. And, since Fedora is cutting edge, it has a short lifecycle per release. Each release is typically supported for 1 year, then updates are ended. And every 6 months a new Fedora distribution is released. You can upgrade from release to release, or you can also skip a release and upgrade to two releases ahead (i.e. Fedora 14 to Fedora 16). Upgrading typically goes pretty well, and retains all user and configuration data so that you can upgrade the software and retain your settings from version to version.
Next I want to talk about Red Hat Enterprise Linux, which is the commercial version of Red Hat's operating system. Fedora was the free version, (Red Hat Enterprise Linux) RHEL is the non-free version. Why is it non-free? Because Red Hat offers support with any purchased version of RHEL. But, in addition to this, RHEL is not cutting edge either. Why? Because Red Hat uses the Fedora distribution that is released for free, and bugs and other issues are ironed out for years (or months), until it is considered very stable. At that point, Red Hat uses that software and bundles it as RHEL. So, Red Hat gives Fedora away to the public, and in return the public tests it extensively and works out all of the kinks, where Red Hat can then release a completely stable operating system which is RHEL. So, even though RHEL is not cutting edge, it is considered rock solid and is very good. Red Hat targets businesses with RHEL, and for good reasons. RHEL is usually used on servers in most cases, but it can be used on desktop systems as well. The lifecycle for RHEL is long, at 7 years for bug fixes and security fixes, and an extended 3 years of support is also added to give a grand total of 10 years.
And finally, let's look at CentOS. CentOS is a free version of Red Hat Enterprise Linux. How can it be free? A third party compiles RHEL from the source and releases it as a separate distribution. Red Hat allows this, and as such I consider CentOS to be one of the best distributions for servers because it is absolutely rock solid because it is based on RHEL. And, it is free. There are a lot of end users that do not need support for RHEL, but would prefer it for free, and that is what CentOS provides. CentOS is basically like the old Red Hat Linux before Red Hat split it off to the Fedora branch. It's great stuff. What I really like about CentOS is that third party packages that are built on RHEL will work on CentOS, because they are two in the same for the most part. And, with both CentOS and RHEL, there is a third party repository called RepoForge that supplies extra packages that are not included with the default RHEL or CentOS. It is also enabled so that the Yum updater can then locate and install packages directly. Support for CentOS can be found at the CentOS Support Forums. The lifecycle for CentOS closely follows that of RHEL, and is currently 7 years for bug fixes and security fixes.
In conclusion, it is up to you to decide which distribution best fits the system you need. I prefer the free distributions as I end up finding free support on forums, which include Fedora and CentOS. For workstations, I prefer Fedora as it provides the cutting edge software and tools. For servers, I prefer CentOS because it provides rock solid stability and a long lifecycle per release of RHEL. As always with GNU/Linux, you can download and try the free distributions and give them a test run. Decide if you like it or not, then go from there. All in all, this is great stuff and I urge you to give it a try.