As people who have asked that question before, you'll probably get the same answer: There is no such thing as "best Linux".
I'll try to spare you the details (which I don't really know myself anyways) and sum it up as simple as possible so you can decide yourself.
Linux does NOT spy on you. Unless you are using a special build, the Linux is open source so it is not a doubt.
Different versions of Linux are called "Distros". There are hundreds of Linux distros that are actively used by people. But, as far as I know, there are 2 Major Linux: Debian and Arch Linux. Many other distros are based on those two. For example, Ubuntu is based on Debian, and Mint is based on Ubuntu. There are other distros with rather original names like Kubuntu and Lubuntu :)
So Debian >> Ubuntu >> Mint...
or Arch >> Manjaro... Distro Watch
shows general view popularity of the distros (not necessarily correct) and you can get a brief info about them.
Mint probably has the most regular users worldwide probably because of 2 reasons. It is based on Ubuntu so anything that works on Ubuntu will work on Mint and it has a much easier and elegant experience than Ubuntu.
That also answers your last question. Not everything works on all Linux.
I triple boot Mint alongside Manjaro and Windows 10. On Mint and Manjaro, you can install 2 ways.
1. Mint and Manjaro have software centers. You can directly go there and install a program you like simply by clicking install. Just like you would do on android mobile phones. Btw, Android and Linux are relatives and they use very similar kernels.
And Just like android, everything is updated via the Update Manager.
2. You will, of course, won't find all the programs you need in the software center, or in some cases you find it but it is outdated. There are again ways to install a program outside of software center.
2a. For Mint, you can download the ".deb" file of the program. That's like the ".exe" files on windows. You simple double click and the program installs.
2b. You can add the program's source into your software center. Then you can easily install it just by updating it. You can do all these via the terminal ( the CMD equivalent of Linux where you type commands but much MUUCHH more powerful.
2c. You can download the source code and build it yourself. I do not recommend that to new people especially if you are not tech-sevy. Things can go south really fast. The Internet is full of such cases.
Ubuntu (and distros based on Ubuntu) are especially popular now since STEAM and as far as I know, GOG officially supports it. Finally, find adamhm's linux guide in this forum.