Man, people, history so easily forgotten.
98 was a great platform, and was about the time I started dealing with administration. Configuring LANs on 98 was no simple task like it is today, but the OS was solid, and ran like a charm for ages. Even gave you that great copy of Weezer's Buddy Holly music video and a few games beyond the usual minesweeper and solitaire.
2000 was an okay platform, but corrupted easily and to date was probably the most hacked / compromised OS.
ME, well, I believe XKCD puts it best: Windows ME and Balmer's Peak
. This had to be the WORST OS MS put out, since they weren't ready for XP, and people were itching for a new OS after 2000's meltdowns.
XP was a great workhorse, still used in a lot of places. Not too many complaints from me. Worked wonderfully, was easy to manage with Group Policies, and most people could use it with minimal training.
Vista - like a nagging ex wife or overprotective mother. Are you sure you want to do this? Never bothered to use Vista, since I had read plenty of papers, reviews and such during the beta stages, and knew I would never transition a corporate environment to Vista.
7 - Beautiful, elegant, and operational. No real complaints, been on it since beta, works like a charm!
Worst is ME, followed by Vista, then 2000...