In my opinion, I think the best episode of Spongebob Squarepants is "Band Geeks".
It had the right humor, Squidward didn't get the short end of the stick for once, and it had possibly the best song of the series in it. If I had met someone who had never seen Spongebob, I would show them "Band Geeks" because, seriously, this episode represents the whole series.