Windows 10. Windows 10 is by far the least resource-greedy modern Windows operating system.
Incidentally, no standard user should be running anything except Windows 10 on their computer, if they choose to have a Microsoft operating system at all. Anything before 7 is entirely obsolete software; Windows 7 doesn’t receive security updates; Windows 8 is just absolute garbage, and Windows 8.1 is basically Windows 10-Lite with some irritating leftover trash from Windows 8. Just use 10.