Tiger is pretty good. I don't have Jaguar or Panther to compare with, but after a number of years of running 8.x and 9.1 on various pre-G3 Macs, I was surprised to find that Tiger is really quite useable on a 500MHz iBook. In fact, if you limit the number of open apps, Tiger on the kids' 500MHz is pretty comparable to my 1.33 iBook.