If you were trying to convince a Joss Whedon virgin of the writer-producer-director's televisual genius, you could do a lot worse than this list of the "25 Best Whedonverse Episodes" assembled by EW. I could quibble with the ordering-- as good as it is, I suspect Firefly's "Our Mrs. Reynolds" benefits more from its Mad Men connection than its own inherent quality--but there wasn't one episode listed that I could disagree with, and that's a rarity when it comes to the intense passions cult shows like Whedon's tend to inspire. Every show is represented (even Dr. Horrible!), and reading through the list made me want to break out the DVD sets again, which is really what these kinds of exercises should, in the end, inspire.
Oh, and their number one choice? It wouldn't be mine-- I'd go with their #2-- but it's certainly a brilliant episode, and a reminder that Whedon's greatest contribution to television is remembering that the scariest demons we face are also the most human.