In my experience, 98 will work with the most games, no matter what you do, 2000 and XP are NT underneath and won't necessarily work with all games. 98 is also less stable than 200 and XP(sometimes) so it's a trade off. Linux overall i think is the best OS all around. As soon as it becomes widely accepted, you will find more good apps for it.
Between linux flavors, Red Hat would be best for the linux hard core and Mandrake is the best for those new to linux because of it's handy VERY user-friendly interface.
Between windows, 98's best for games and XP best for business. (If you want a good Imaging workstation get a Mac.)
Lindows (if it ever flies) has the potential to be great but it all depends on how popular it becomes and how much press it can get. Marketing is what can make or break a business.