[Matrixbeast]

Oh man, Sisterhooves Social is an amazing episode. It showcases the sibling rivalry excellently and has awesome moments from every episode. Easily one of my favorites. I liked that they didn't force any one character to be an antagonist in the episode. While Rarity was more of one, it did well enough to show that siblings clash, and, more often than not, neither one party is entirely to blame.

Also, interesting that Sisterhooves was what won you over to the CMC (Like I said, they'll always win you over...Eventually ), despite Scootaloo (Most popular CMC character) being absent entirely, and the episode focusing more on Sweetie Belle than Apple Bloom or the group as a whole.

Aping your idea, though, I'd have to say my 10th favorite episode was Secret of My Excess.

It was the kind of episode Spike needed and it was a rather touching one. The moral of giving vs. receiving wasn't too heavy handed and the antics of controlling Spike was fun. Spike admitting his crush was a touching moment, Rarity choosing the Fire Ruby over her life on the basis that Spike was the one who gave it to her (Note: Rarity didn't know the dragon was Spike and no one else could hear her. Everything she said in that moment was the truth) was heartwarming and the episode overall was a mix of smiles, action, and heartwarming moments.

Spike isn't the most popular of characters, but it was a massive step up from the typical Spike story of "He's just a baby" being the driving point (Like in Dragon Quest or Owls Well that Ends Well).