I'm using VirtualBox too to host multiple Linux based servers.
Before implementing/upgrading a guest, I make a backup of the guest. Unless, I'm install a new guest I don't need a new image.
My Linux OS of choice is POP!_OS for the desktop.
Discussion
Nice! I tend to usually lean towards server side, because I prefer command line over GUI for most things.
For Desktop, I usually use Ubuntu or Debian, but once and awhile I'll peak distrowatch.com 👀👀