I still have my XP Home (2005)... now my Husband's computer, so he (who has no knowledge) can use it, and only it
My XPpro (laptop- 2006) has been doing all my testing and come through with no scars ... it's been upgraded to Vista Business and is still the "Champ"!
MY Windows 7 Ultimate started out as Vista Ultimate (custom made for me - 2008). It, too has done plenty of testing...This one is mine, and nobody but me touches it
In all, my experiences with XP and Vista have been pretty fantastic over the years.