A lot of shows I’ve seen through to the end typically peak during the second and third seasons. This is because I generally don’t invest my time into long-runners anymore, so I feel the most comfortable putting on an episode from a little over halfway through something’s brief but powerful run. The Simpsons is an outlier to this vibe, since my favourite season of that show is the sixth.
I voted Season 3, because that’s where I think both The Powerpuff Girls and Rocko’s Modern Life shone their brightest, but those are just two examples.