Arguably XP has been MS' most successful OS.
Even ~15 years after its release, it still has as many users as W8.1 and W10 (~10%).
I first installed XP SP1 in 2004.
I did have some problems with malware, but nothing like W98SE's malware problems.
After I stopped using IE6 and swapped to FF (in 2006) the malware problems went away.
I swapped to W7 in January 2010.
I still have XP installed on another PC, so that I can use Windows Live Photo Gallery.
I also have an XP VM for my old games, because a lot of them don't like newer versions of Windows.