There are many distributions, so many it's impossible to know them all, let alone test them. Anyway, here you'll find no tests. These pages are only my feelings about them.

Debian GNU/Linux

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Debian's first stable release was made in 1996, and as now (2020) we are at version 10. Debian's name indicates the system might be powered by another kernel than Linux - However, "HURD" was alpha back in 2009 and... still is!

There are three versions of Debian at any time: Unstable which is a developpement version, Testing wich is the future stable, and Stable.

While not really reserved to geeks, Debian does not try to be "beginner friendly", nor is it cutting edge (at least stable). It takes some time to really understand and know it, but the result is well worth the effort. It uses apt-get to install packages and supports most Desktop Environments - including Trinity Desktop :)
It's very difficult to change once you've learned to love it.

It's a very solid distribution that gets the work done. The next version is always ready "when it's ready", so it's no distribution for lovers of the latest and greatest.

One of my two favourite distributions and the base of many derivatives. Try it!

Note: since "Jessie" Debian uses systemd. As a result, there was a fork to maintain a Debian without systemd: Devuan. At the date of this writing Devuan ascii is Debian 9 without systemd.
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openSuSE

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SuSE is the most important Linux distribution for me. Historically, SuSE teached me Linux. Back in 1998, they sold their distribution with one of the best manuals I've ever seen (You can read or download it's successor here). I learned by reading and doing, and after a few month I dropped OS/2 for Linux. It's 18 years ago and I've never looked back.

SuSE started using KDE at version 0.4. It's an RPM based distribution but has little to do with Red Hat - it seems the origins were rather Slackware.

The oldest CD's I own are from SuSE 6.2, although I started with 5.2. Since version 10 I was not always satisfied with openSUSE but still regularely used it, as it's one of the best distributions on laptops (at least on Thinkpads which are my favourites). Currently openSUSE is at Leap 15.1

Compared to Debian, openSUSE is more "up to date" as far as hardware support goes. I like YAST as a global administration tool, and although I would still prefer apt-get, SUSE offers yum and zypper that are very efficient when you know how to use them.

If you are serious about learning and mastering Linux, I'd suggest you try openSuSE!
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Deepin Linux

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Deepin Linux is a chinese distribution, originaly based on Ubuntu, now based on Debian (stretch). Deepin proposes an easy to install and easy to manage distribution. They have developped a special GUI (Deepin DE) that, by the way, you can install on other distributions. I'd say it is "Mac like", with an app-store and well presented settings.

After converting my wife from Windows to Mac, Deepin let me convert her to Linux. If you are looking for a "Linux for newbie", I'd suggest trying it.

It's quite graphic based however so not for an older machine. Deepin's DE proposes a MAC-like dock. When you click on the settings icon good looking settings slide open from the right side, all settings are easy to use, changing the system's language is easy as well. I was even able to setup pinyin to type in chinese - a requirement for my wife -better than on the Mac, much better than on Windows (which required a chinese programm that looked like a trojan horse). When my daughter asks for a computer, I'll propose Deepin.

The app store makes it easy to browse and install programms - but you can apt-get install them too, it's Debian under the hood.
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Gentoo

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Gentoo... That's another story. Anything but a beginner's distribution, any Linux enthousiast should give it a try.

Most distributions install everything: Gnome and KDE, every module (= driver)...
The result is that it will run on any  hardware, but it is BIG.

Gentoo let's you install only what YOU want. It does it by building the complete distribution from scratch. You'll compile almost every part of the software, with total control on the flags: with KDE but without Gnome, or the opposite. With Alsa but without Mono. And do on. And you get rolling updates so you should never have to install again.

Gentoo is loved by those who want to compile a system for special tasks, special computers with limited power. But it's also a great way to understand how a distribution works. By following the guide, you'll discover bootstraps, understand when to load what, what chrooting means...

Gentoo uses a very special packaging system, ebuilds, that are installed with emerge.

You should give it a look. If Gentoo is too much for you, try Sabayon: a rolling distribution compiled from Gentoo and all set up for multimedia.
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Ubuntu Linux

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I don't like Ubuntu. Why do I mention it here? Because I'm sure people would ask why I forgot it. I did not. I used Ubuntu (10.10) for about a year when KDE 4 drove me away from SuSE and I tried to adapt to Gnome for a while.

Ubuntu is considered a Debian derivative, but it's so much derivated that almost no Ubuntu package can install on Debian. Ubuntu is made with the will of being "easy", "beginner friendly". This means it's makers make the decisions for you, tell you where to go and how to do it. They use sudo much as OS X does. You can get a root account but that's a mess because the sudo behaviour remains. It's interresting to see that many distributions that originaly based on Ubuntu went back to Debian...

However, Ubuntu is still Linux: if you digg and search you can tweak it to behave like a sensible Linux, but why bother? There are so many better distributions to choose from. Most Ubuntu users I know are bad Linux users, because they actually don't understand how their system works, because they did not have to learn. Ubuntu produced stupid Linux users like there are so many stupid Windows or Mac users.

But this is my point of view - feel free to try Ubuntu!

And if you like Ubuntu but hate Ubuntu, take a look at Linux Mint which is an Ubuntu derivative.
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