First OS I technically used was DOS, since you need to into DOS to get to Windows on my old computer..
The second OS I technically used was Windows 3.11 (notice, two 1's) for Workgroups.
So, I voted Windows 3.1
(Windows 3.1 is just Windows, 3.11 is for Workgroups with domain join and advanced networking)
Why did we have the Workgroup version? I have no idea.. I think it came from Dairygold (used to live on a farm)