XP is stable...and you don't have the UAC (User Annoyance Control) to deal with.
By using non admin account for most activity when on the wire reduces many risks along with a good antivirus / antimalware tool.
Outside of the office I use it and will continue to use it for programming radios (HAM and my volunteer fire department).
Some older software that I need to run will not work with vista or later platforms.
I even have to keep DOS available for some tools. Fortunately dosbox handles most of that.
My biggest problem are the new laptops without a real serial port (rs-232). USB to RS-232 converters are hit and miss.
Some software can't handle the higher port numbers. Prolific chipsets (especially the chinese clones) are problematic.
Windows 8 ? My exposure to it has been not well received. If I had the chance I'd re-image those machines to 7.
In the end, I retain backward compatibility to Dos 6.22 and Win 95 and XP.