I have a friend in Bratislava,who uses Windows XP today as main OS on all his PCs including his main machine.He expressed,he will never accept anything else.
For the comparison I have Windows 7 as main OS on my main PC & all other,where it also is...usually in multiboot.Most of my newer machines has multiboot containing also Windows XP & Windows 8.1,but if present,Windows 7 is set as main OS & older machines have often Windows XP solely, XP+DOS,XP+Win98SE,or so,& the absolutely oldest(286) have DOS 3.30+Windows 1.01 & 386s usually DOD 5/6/6.22+Win.3x,always as most era correct to the HW,with the exception for newest machines-i go never behind Windows 8.1 & if possible,I have Win.7 there too,& if present,I set it as default OS.My main PC I got with Windows 10.The 1st thing,I did with it,I replaced(upgraded) the HDD & "downgraded" to Windows 7(+FreeDOS with Win.3.1+Vista+Server 2008 Enterprise 32bit,which can access whole 10GB RAM & run 16bit apps @ 1ce),later I added 2nd HDD with Windows XP & some Longhorn pre-reset builds...due to curiosity...
So I have XP on every PC from P4 above & many instances on older PCs too,but my main is 7,but I know persons,who has such feelings(hatred) also to Win.6/7/8(.1),as I have to 10+,thus XP is their 7 & my most used install media is Windows XP Professional-Corporate,because beside my own usage,my friends & other fellows borrows it from me...They never asked other install media,but this 1 very often,so Windows XP Professional is sure most popular within the retro community,& the Corporate ISO is the easiest way to install XP now,as it is impossible to activate it normally nowadays,thus U have 2 opinions:save an old PC with original HDD & OS,or...& this is most common,U found an old PC with empty HDD or no HDD & then this ISO is the best way of getting it back alive.
& b4 U call cops on me,I announce,that in Czechia the laws for abandonware r same as for freeware,thus until I share the ISO of an EoL SW for free,I do not brake the local laws,I would only become criminal,if I would ask money for it,which I do not,I am doing that for preserving old OSs,not for profit,for me it is like with endangered species,I spread them to prevent extinction,if I will be killed,my friends will have backup & vice versa,the goal is no1 will exterminate old good OSs,& until I do not gain profit of it,I do not brake local laws by gifting abandonware,so if U will call cops,only thing will happen...the cops will have a good time playing Commander Keen,Tank Wars,or Lotus in my living room...I guess,they will most like Lotus...