Though all of these episodes are fantastic in their own rights, I would have expanded the list to maybe a top 10, and I'd have added Ragnarok & Roll to it. It's one of the most character-driven and emotionally-charged episodes of the whole series, with J. Michael Straczynski once again shining as the best script-writer on the show.
When the team are confronting Jeremy (the big bad) on top of the Carstairs building, proton packs ready for simultaneous overload, saying one last farewell to each other as they know it's a suicide tactic, the one word you hear from Egon is "Janine". As a kid, I never really got the why and how of that one name, but having grown up (nearly 27 now) and having absorbed more of the Ghostbusters mythos, it's a poignant little bit that sometimes gets overlooked. Janine (up until GB2) had always carried a torch for Egon, and in that split-second, we discover that he feels the same way about her.
Just my humble opinion. I'm a big softy at heart, really