We have two laptops and a desktop that run just fine on Win XP and my wife's install of 7 needs XP mode to run much of her business software - and we don't really care about MS not supporting XP. The computers on XP do everything that we need them to do and work well.
Windows 8? MS has already seen the error of their ways. 8.1 they make to run more like 7. Just go with 7 if any upgrade is necessary. Win 7 is OK as long as you have a version with XP mode - since there is some software that does not play nice with 7 on its own.