For desktop computers, either Windows or Linux. Windows on my main computer since I rely on so much Windows-only software (MS Office, Many Games) despite the BS that Microsoft does to windows in new versions, but Linux has gotten way better lately, especially as it picks up new users as Windows declines. MacOS to me the worst of both worlds when it comes to lack of software support and corporate BS
For Mobile, definitely Android. Android is what I wish Linux was for Desktop computers; Loads of software you can get from many places, open source, and not locked down. It’s mainly the way it is because for Mobile OS’s, Microsoft was spending too much resources shooting itself in the foot with the Zune than to make the necessary improvements to make Windows Mobile to be competitive, and by the time they realized their mistake it was too late. iOS is such a pain in the ass for me to use due to how locked down it is, and while it has more software support than MacOS, its locked down nature and being mostly restricted to getting software from Apple means that several apps that I rely on (including a few apps not on the Google Play store) will never be available for iOS. I also like to see where every single file on my phone actually is
Trisquel GNU/Linux
https://trisquel.info/en
Because it is a fully free distro, which is important to me.
I use Trisquel because it is the most user friendly I’ve found in the free distros.
Some hardware drivers are unavailable, but that’s fine, just transferred away from non-free hardware.
For compatibility, usually export to PDF.
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Also GrapheneOS on phones and tablet. Has less nags and bloat. Privacy centric mobile OS.
It’s nice to see such a willpower to use fully free distro. I am often prevented from using a fully free distribution only by the non-free firmware for AMD GPU.