I would say anything from season 1 - 10 (season 1 being the weekest of them all). Within that time frame of seasons there are some of the most classic episodes in cartoon history.
I am about halfway through season 1. If it is the
weakest of the first 10, then I have some real treats ahead of me, because it is great!
(Not sure which season it is in, but the funniest episode I have seen is the one where the Simpsons visit Epcot Center. The electric car, in particular, is hi-freakin'-larious!!
)