I now own Series 3 to 8 of the Simpsons on DVD. I'm trying to remember if that's all the ones worth buying or if I ought to get 2, 9 or 10 in the future.

When were the peak years and when did it completely tail off entirely?

I'm pretty sure I remember Series 11 as having a lot of ropey episodes but can't remember if 9 or 10 are worthwhile...