XP all the way. Far superior to 98. No way could I ever go back to 98 after using XP. It just handles everything far more efficiently, especially resources/memory. Night and day.
I had never used 2000 before but did mess with one computer with it installed after I had XP for awhile. No way could I use 2000 after using XP.
I have XP Pro on 4 computers, no problems with any of them. 2 of them clean install, 2 of them upgrade. All stable as a rock.
BTW I am a gamer as you can see by my system below. XP has not slowed my gaming experience one bit. Only issue I have is the refresh rate issue. I edit my own driver infs so I'm good to go there also.
I7 3770 @ 4.4 gig (Noctua NH-U14S Heatsink), ASRock Z77 Extreme6, 16 Gigs (2x8) Corsair Vengeance DDR3 1600, EVGA GTX 680 Signature 2, Acer P236H 23" (1920x1080), X-Fi Xtreme Gamer Pro, 2 WD 640 gig SATA HDDs, WD 750 gig HDD (eSata), WD 1TB Black HDD, Sandisk 32 GB ReadyCache SSD, 2 SATA DVD Burners, Logitech Z-5500 5.1 Speaker System, Corsair TX750w PSU, HSPC Top Deck Tech Station, Windows 7 Pro x64