My go-to system now is Alpine Linux, though I might do an Ubuntu or Windows 7 setup just for the very occasional gaming. But as a favorite, as in a system that I really enjoy even if it is a completely nonsensical decision today, then Windows XP.

I have a laptop running XP Pro SP3, and a mini PC running Windows Server 2003 Enterprise so I can experiment with both, and using XP is always fun while using a Linux system just feels… boring, utilitarian. I will find fun things to do on Linux but it probably won't be too related to the system itself, but on XP I explore its APIs a lot, try to document some undocumented features, or just bask in the nostalgia. I create weird software to compensate the stuff that no longer works (like this or this), or to see just how much it uses JavaScript (accompanied by this), or to avoid using the web browser since that's heavy (this or this or this), or to explore other things like a GPS.