There is no best OS, in the sense of one-size-fits-all. Do you want privacy? Then use Kali Linux. Do you want to play games and be able to run just about any program? Then you want Windows 10, with privacy optimized, which is the opposite of the default installation. If you don't want Windows, but want an easy to use one of the free Linux distros, try Linux Mint. I find Mint to be the simplest to set up and use of the over 1000 distros available. Ubuntu is also popular, but has a different style UI, sort of a blend of Chromebook and Mac desktop looks. I personally use Linux Mint and Windows 7 and 10, since I own a computer shop that builds and services PC's. I don't work on Macs because Apple is an elitist asshole-run company. Out of ~1000 customers of ours, only three use Linux. Most of the rest use Windows, from XP through 10. The remaining ones use Chromebooks and do just about everything in the cloud. New 2019 model Chromebooks run Android apps. You can use flash drives or DVDs to boot to live versions of the Linux distros to run them without having to install them. So, you can do so without a storage drive mounted. Test away!