For me, I guess it would be my current Win98 machine. It's a Dimension T550 with a Celeron 1400, 512MB of RAM, Voodoo3-3500 @ 193MHz, Aureal Vortex 2 SQ2500 PCI sound card & AWE64 ISA card. I've been using it for Win98 and late era DOS gaming since 2012, and -- believe it or not -- have been running the same installation of 98SE since 2017!
Mid-2000 being my cut-off point, not once have I ever felt the need for more speed. It's just a reliable, performant, and compatible machine that's never given me any trouble during my Sunday morning "time machine" gaming sessions. I just love the dang thing! Oh, and the 2017 reformat? Totally my bad; I managed to bring in a virus via some old shareware diskette...yikes!
And you know what? The 80GB hard drive is roughly 75% full, it's never been defragmented, I've installed/uninstalled/reinstalled games countless times, and I even keep it connected to the internet. Yet, the 7-year-old installation of Windows 98 just keeps on going. I feel as if I've won the Win9x lottery or something! Knowing just how fussy 98 can be with even slightly newer hardware, I'd be concerned about going much newer than a tried & true Tualatin or Thunderbird system.
"A little sign-in here, a touch of WiFi there..."