The choice of distro is depending on many factors, many users decide for their distro based on the following criteria:
- comfort: is it a rolling release distro, or will version updates still be necessary. Advantage of rolling release distros is that you never have to reinstall, well, that is until the shit from experimenting is piling up so high you need wings to stay above it, and you reinstall just because you want a functional system again. Some distros have version releases, but also an automatic update utility that makes it unnecessary to reinstall. Arch/Manjaro, Gentoo, OpenSuSE Tumbleweed, etc, are rolling release distros, most other distros are version release distros, Fedora is the odd one out, as it has a reliable automated version updater called FedUp, that avoids having to reinstall, having to sort out repos, having stuff break, etc...
- Features and Speed: newer is mostly better, for desktops, it's nice to have bleeding edge features. Pretty much all distros can be made as bleeding edge as you want by enabling testing or unstable repos, but one distro's bleeding edge is another distros stable. If you want bleeding edge, Fedora is the most bleeding edge with rawhide, the fedora stable is about as bleeding edge as Arch, but there is often breakage in Arch, and Fedora stable is two generations of testing old by the time it's in Fedora stable and pushed out in Arch, because there is Fedora testing and Fedora rawhide before it. Unstable in Arch is for adventurers that really like volatile code and heavy breakage, but hey, that's fun too, and someone's got to do the testing...
- Bloatware, bad/ugly packages, proprietary code, tainted kernels: some distros are "liberal" when it comes to integrating non-open source licensed software in their version of the linux kernel or their packages. Some users want to use non-OSS software for whatever reason, and they might prefer such a liberal distro like Manjaro for instance, because even with a tainted kernel, Manjaro will still offer a certain degree of support for their distro, even though that is technically very difficult, because you can't debug closed source code, and even if the code is open source but the license isn't, that means debugging such code would still be illegal. A benefit of liberal distros like Manjaro is that they offer a working "out-of-the-box" experience with things like proprietary graphics drivers, whereas if you would want to install these on clean distros, sometimes that might present somewhat of a challenge. Another thing is that some distros, like Arch or Gentoo or Fedora, are lean and mean, they provide a minimum of preinstalled packages, to keep the base system superfast and transparent, other distros, like Ubuntu, Mint or OpenSuSE, prepackage a lot of bloatware, "suggesting" that the user should use this or that application software instead of something else from the huge collection of FOSS applications, because they have a deal with some company, or because they have optimized or hacked that particular application to fit their theming or system settings.
- Ease of use: some distros have much better package managers than others, and have much more mirrors for their repos than others, or have applications that offer ease of use and practicality when accessing the repos. Fedora is the absolute king of ease of use in that respect: yum is by far the most powerful package manager, and it's successor is ready to go with many new features, speed and reliability improvements. Yum uses Presto, which means that Fedora will only use about 10-15% of the bandwidth of other distros when updating, and it uses fastest-mirror, which, together with the literally hundreds of official fedora/redhat-repos all over the world, offers an incredible ease of use when it comes to code and software access. Another aspect of the ease of use is the packaging. Some distros package very carefully, and have very strict rules when it comes to packaging, so that all libs and deps are perfectly covered and there is no breakage, and so that only libs and deps from the official repo are used, and no hacked up code. Again, Fedora is king when it comes to packaging quality and repo hygiene. Gentoo doesn't package, everything has to be compiled from source by the user, and that's the diametrically opposed position, with minimal ease of use. Advantage is that the software will always be perfectly compiled to suit the system, and that shows in terms of system speed, Gentoo is the fastest linux distro. Other aspects of ease of use of a distro include: the daemon system, does it use a modern easy to manage system like systemd, or does it use a legacy system, does it use the new more logical system tree or the legacy one, etc...
- Security: there are many aspects to security. First of all, there is the aspect of open source software: a distro can opt out of closed source software or even non-GNU/GPL licensed software. Debian, Fedora, Arch, Gentoo and Slackware, that is all the main distros except OpenSuSE, have strict open source code policies. OpenSuSE has the same policy, but makes some exceptions, most of those exceptions are still open source code but not open source licensed software, like Xen Hypervisor for instance, other exceptions are less harmless, and involve code that is neither open source nor open source licensed, and is the product of a license deal with Microsoft from the 90's, when Corel bought SuSE from it's German developers, but met financial hardship, and sold out to Microsoft, and when Novell acquired Corel, they inherited the license deal with Microsoft, of which the extent is not exactly known. In general though, there is no hidden code or something in OpenSuSE, and Microsoft has not yet shown any aggressive behaviour because of this license deal that hangs above Novell's head like a sword of Damocles, but it is still very well possible that some day, Microsoft will use that license deal to either make an instant entry into the linux market, or to harm the linux community to protect their legacy closed source software console.
Second of all, security has a lot to do with system integrity. Some distros come out of the box with a fully integrated security suite. Best example is Fedora, that comes with SELinux, which is the most powerful MAC, and with policies for every application in the repos. This is a huge feat of software development, and that dedication to security also shows in everything else: Fedora was the first to integrate firewalld to replace iptables, and for the next version, the successor of firewalld, the next generation of netfilter, is ready to go. Fedora devs are drilled to be very security-aware, checking every bit of code and license before letting it in the repos. This goes far: TrueCrypt for instance was never allowed in the Fedora repos, the code was analysed and recompiled, and Fedora has it's own alternative, RealCrypt, which has no licensing or security issues. Another example is chromium, which is not allowed in the official Fedora repos because Google has hacked open source packages from other people to put their browser together, and has not been respectful and consequent in doing so. This makes the code less transparent, thus potentially dangerous. Another example is Steam, which is closed source, but is basically a hacked up version of an old firefox browser, which is open source. Of course Steam is not in the official Fedora repos because it's not open source, but it's offered by RedHat devs in private repos, just like Chromium. RedHat devs are so trained for security, that they have merged the p11-kit in the Steam client for instance, which prevents the firefox application on which the Steam client is built, to access the Mozilla Trusted CA list, that may be used by the normal, open source, firefox browser that is the standard official open source browser in Fedora. The p11-Kit forces the firefox to which it is glued (in this case, the hacked up old firefox 9 that the Steam client is), to use the system CA list (to which it has no modifying permissions) instead of the Mozilla CA list, which is in the home directory, and thus could potentially be modified. The Steam client also comes with it's own very strict SELinux policy. No other distro goes through so much trouble to maximize the security. Of course, this security may be cherished by some users, but may also be hated by others. Many users that install non-OSS packages, but still want to use Fedora because of the bleeding edge features, speed, and stability, set SELinux to permissive, or even switch off SELinux, because they don't like being notified of security protocol violations of such non-OSS programs. Other distros like OpenSuSE, rely on the legacy AppArmor to offer some MAC-like functionality. Ubuntu also has AppArmor, but all profiles are disabled by default, and it's up to the user to enable even elementary profiles like the firefox profile, or to make them theirselves. Still other distros may have the kernel modules that enable the use of things like AppArmor, but it's not included by default, like Manjaro for instance, that doesn't have SELinux kernel headers, but has AppArmor kernel headers, but AppArmor is not really available for it either. In those distros, Tomoyo or Akari may offer a security solution. Especially Tomoyo is pretty powerful without even demanding kernel headers, it works on every distro, and it can compile it's own application profiles by a self-teaching system the user can start.
Thirdly, security also has a lot to do with offering a secure way to handle unsafe software, like the Steam client or Skype, or known malware, like Windows. Some distros have more tools for that than others. Things like virtualization functionality, linux containers, netfilters, journals, etc... all play a role in this, and the more of these tools a distro offers in the official repos or prepackaged, the more options the user has to safely run dangerous software with minimal risk.
I personally think that it's a good thing to constantly try distros out. I use RHEL in my office, and Fedora on my personal PC's, because for me in my use case that's the best solution, but every time a new version/milestone of any of the main distros (new version of Slackware/Vector, OpenSuSE, Debian, Mageia/ROSA, RHEL/Fedora/CentOS, or a new milestone in Arch/Manjaro or Gentoo) is released or reached, I install it in a kvm container and check it out. I even check out distros that don't belong to the first tier, like Ubuntu or Mint or Kali or Kororaa or Qubes-OS, etc..., or that aren't linux kernel based, like FreeBSD/PC-BSD. Just because it's nice to know what's out there, to know the options, to know how their package manager works, what base functionality they have, what focus they have, what speed they have, what stability they have, etc... I personally think the two best quality distros are Fedora and Arch, with Debian only just behind them because it's not bleeding edge, but I also think that all 7 main "top tier" fully-FOSS distros (Fedora/OpenSuSE/Mageia/Slackware/Gentoo/Debian/Arch) are great products that are so far ahead of any derived distros in terms of intrinsic overall quality, that any one of those is a very good choice as a daily driver, depending on the user's use case. I also like some derived distros, that show great quality even though they're not top tier, like Xubuntu and Manjaro. Xubuntu constantly knows to stay well above Ubuntu in terms of quality, even though they have minimal means. Xubuntu always seems to be able to make the most out of the Ubuntu Core, whereas that seems mission impossible for Ubuntu. Manjaro is still pretty young and lacks a bit of maturity, but it shows incredible promise and is a "next generation" linux distro, very user-centric and bullshit-free.