Choosing the right OS (operating system) is much like the presidential election for most people. They choose the better of the two most popular (and in many people's minds, the only) OS's. But are they the best for you? What are some alternatives?
For your computer
Let me first say that there is no single operating system that is best for everyone. It all depends on your preferences. I'll make a general list here and if anyone wants me to explain more about a specific OS, just comment.
Microsoft Windows: The most popular OS by far with over 1.5 billion users, Windows has been leading the market for years and is the OS of choice for most people. Windows is easy to set up and easy to use and understand. However, ever since the release of Windows 10, people have been looking for alternatives. Microsoft is openly spying on users and many updates that introduce spyware are breaking some software.
Target user base: Your average Joe and Jill, some slightly more advanced users.
Apple Mac OS: The strong second-most popular OS is Apple's Macintosh. Its very similar to Windows in ease of use and easy setup. However, it limits the user more than Windows, so there is less freedom to customize and do some advanced stuff. Thankfully, it doesn't spy that much on you, so many people might favour Mac.
Target user base: Your average Joe and Jill.
Linux: Now we're getting to some less popular yet better (in my opinion) OS's. Linux, contrary to popular belief, can be just as easy as Windows or Mac to set up and use. There are quite a few versions of Linux ("distros") which offer unparalleled customizability and usability. You can do a lot more with Linux, that's why many "hackers" use it. Linux is completely opensource which means that anyone can see what it's made up of, almost completely removing the possibility of spyware being built-in to the OS. Also, it's completely free. Here is a list of some good Linux distros.
Target user base: Depends on Linux distro, but mostly more tech-savvy users.
For your phone
There aren't that many operating systems out there for your phone. That's primarily because it's hard to change from your stock Android or iOS to another OS. I won't include how to install these OS's here, since I can fill another whole post with that.
CyanogenMod is arguably the best one out there. It's based on Android, but includes many more privacy and customizability features. Each version has to be separately developed for each phone model, but the newest ones are built the lastest Android Nougat.
Firefox OS, brought to you by the popular browser developer, isn't as popular as CyanogenMod and it's still being developed. However, its key feature is that it is built entirely on web technologies, which means that anyone who can develop websites (or use HTML and CSS) can build it.
Ubuntu Touch aims to be a mobile-friendly version of the popular Linux distro Ubuntu. It has a nice feature called "scopes" which brings everything you need to one screen without the need to open and switch between multiple apps.
OmniROM was created in response to the perceived commercialization of CyanogenMod. The developers of CyanogenMod refused to implement a feature that would majorly increase users' anonymity. I don't know much about this OS, but it seems to be a good alternative to CyanogenOS.
I using Windows 10 on PC, Windows 8.1 on tablet and Android on smarphone ;)
CyanogenMod is no longer in development; the new project is called LineageOS.
Also, there is an Android OS for PC called Remix OS (for everyone out there who wants to check out some experimental stuff). There still are some issues, but looks like it will replace those horrible emulators.
To be honest. Nowadays, most distros are even more streamlined than Windows 10. Win10 is some of the most horrible shit I've seen.... The backend doesn't work, the frontend doesn't work. And the amount of the proprietary closed source shit. My gawd.
I am a big fan of Linux Mint on my computers. Normally, the only drawback I find is problems playing multiplayer games with my daughter and brother, since they both use Windows.
For my work (I teach Microsoft Outlook) I need to use Windows as that's where Outlook runs natively.
I can definitely recommend Linux Mint for people who want to escape the Windows world without having to use an interface that feels totally new.