To be honest, I follow Linux desktops more closely than Linux distributions. To me, desktop environments are where the innovation occurs. In fact, I would argue that when a distribution calls attention to itself, something is probably wrong.
All the same, I have my favorite Linux distros. They are not necessarily the most popular -- that would be bland -- but they are distributions that, one way or the other, are influential or fill a niche extremely well.
In reverse order of preference, they are:
KDE Neon is my most recent discovery among distributions. It's useful because, for the last couple of years, KDE Software Compilations and the Plasma Desktop have had separate releases, which may useful for developers but confusing for users.
The Free Software Foundation's list of free distributions has only eight projects. All those on the list are free from the kernel on up, but most are small, and slow to release.
One of the more active distributions on the list is Trisquel. Based on Ubuntu, Trisquel's point -- at least for me -- is that there is no particular point to it. For the most part, the average user will never notice that Trisquel is completely free. When they learn that Trisquel's nature, they have to admit that a free distribution is practical, and less of a dream than many users might assume.
For years, Fedora has been has been the leading .RPM distribution, rivaling Ubuntu for usability. I usually have it installed on a laptop, to keep me from being too Debian-centric.
I respect Fedora for its determination to include only free software. Those who want proprietary software have plenty of places to get it, but Fedora has resisted the temptation to court popularity by making proprietary alternatives accessible from the desktop -- a stance that I will always admire.
Given my preoccupation with desktop environments, Bodhi is a natural choice for me. Bodhi was the leading distribution to use Enlightenment, and now develops an Enlightenment fork called Moksha.
Under either name, Bodhi provides a welcome alternative to the leading desktops, not just because it's fast and efficient, but also simply because it's different. I often worry that diversity is slowly draining from free software, but Bodhi provides a welcome exception.
The first distribution I ever managed to install was Mandrake. That was years ago, but I still keep a fondness for Mandrake's descendant, including Mageia. Compared to apt-get or dnf, Urpimi is a minority package tool, but I remain fascinated by it as an alternative.
Even more importantly, Mageia does more than any other distribution to show how KDE can be customized into a desktop of beauty. It's the distribution I recommend to anyone who wants to try KDE.
Tails is a privacy-conscious distribution that can be run off a flash drive. Used with Tor, it provides a quick method of anonymity, although less security than Qubes OS (see below). Project members take privacy seriously, with many using a pseudonym for their contributions.
Despite all the talk about privacy and security these days, both are poorly understand by average users. One reason why I appreciate Tails is that the project has gone to some effort to assemble and write documentation. Even if you decide not to run Tails, its documentation is well worth reading as a primer in security.
Although I try not to be paranoid about security, I do have a healthy awareness of it. Often, I worry that security options are too difficult for the average users.
What I admire about Qubes OS is that it brings security to the desktop, with tools that anyone can use. Using Xen hypervisors, Qubes allows you to create security domains, each with a different level of protection, and each color coded so you can see at a glance how safe it is. To further protect users, routines like copying files are carefully controlled, operating in temporary secure domains, and specifying the source and target domains.
The price for this level of security is a memory overhead much greater than that of a normal distribution. No one will ever recommend Qubes as a means for prolonging the usefulness of an older computer, but it just might be the forerunner of the future.
I have never installed Knoppix to a hard drive, and I probably never will. All the same, I always burn a copy of the latest version of Knoppix, and keep it within arm's reach of my keyboard.
You see, Knoppix pioneered the Live CD. It now offers both a CD and DVD, both with hundreds of packages.
No distribution is handier when a machine needs triage, such as running fsck on an unmounted drive. As a bonus, you can do the necessary surgery in a familiar desktop environment, which is an unnecessary luxury, but a comforting one when you are panicking over an emergency.
First released in 2000, Knoppix remains what it has always been -- as no nonsense as its web site, and as dependable as its Debian ancestor.
Descended from Debian and Ubuntu, Linux Mint listens to users more than any other distribution. Its MATE desktop may be a fork of GNOME 2, but it's a desktop that users know and want. By contrast, its Cinnamon desktop is an original, but never too radical, and never too limiting in its work flow.
In both desktops, Linux Mint has hit the sweet spot. Never too radical, yet innovating in minor ways in every release of both MATE and Cinnamon, Linux Mint is the comfort distro. No wonder it managed to come out of nowhere and manage the difficult feat of becoming one of the leading distributions in the last decade
Debian is the most influential distribution of all times. Many of the major distributions are based on it, including Knoppix, Ubuntu and Linux Mint, and almost two-thirds of all distributions, period.
The reason for this influence is that Debian is all about choice. Like many distributions, it offers your choice of desktops. You can opt for stability or newness. You can make it run a free desktop, or a proprietary one. A few items in its repositories even conflict with each other. Although favoring a free desktop, Debian gives users the raw tools, then gets out of the way.
If you've heard rumors that Debian is complicated or difficult, ignore them. Debian is as difficult as you want it to be. I can't think of any other distribution that offers such choice, or such freedom.
You may notice that any form of Ubuntu is missing from this list. The reason is that I do not care for Unity, Ubuntu's default desktop.
If I were to include an Ubuntu variant, it would probably be Kubuntu, Xubuntu, or Ubuntu MATE. However, KDE, Xfce, and MATE are better represented by other distributions, just as Ubuntu is more a convenient source for a user-friendly distribution like Linux Mint or Trisquel. As Canonical Software become more oriented towards OpenStack and hardware, I am starting to suspect that, like Debian, the Ubuntu distribution is moving towards being more of an upstream supplier than a distribution to choose from.
No doubt many would disagree, but that is where Linux distributions currently are: more desktop-oriented than distribution oriented, which makes any list of leading desktops as idiosyncratic as this one unless it's based on popularity.
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