Raspbianis the official operating system which is the most commonly used one. NOOBSis a much more user friendly OS for beginners built on top of Raspbian. Then we have raspberry pi version ofUbuntufor common use,Kali Linux, Arch Linuxetc. Then you can burn the image on to the SD Card u...
The other bit of general advice I can recommend: a lot of my testing VMs need to be rebooted frequently. Maintain good snapshots, ensure you have an NTP server configured, and EVERY time you revert a Linux VM, stop the ntp service, run ntpdate to sync to your ntp server, then restart...