Every series has some classic episodes and a few that are so-so.
On the whole i love every series (Cartman is the best character ever, anywhere!!).
Again, the latest ones are on Paramount at the moment and some are pretty funny and a few not so hot (but their average episodes are still better than most other programmes best ones).
Paramount recently (a few months back) did a weekend of the top 10 episodes after a big vote. See if you can look those up and watch those first?
Best cartoon ever in my opinion and the film was great too.