Season 1: CMCs. As soon as they start searching for their cutie marks, they start building the Mane 6's past for us as well. There were so much potential here. Sweetie Belle was going to become the best singer of them all, I just knew it!
Season 2: The season of Discord, Read it and Weep, and the Wedding. This is the season of the Bronies. There was nothing that stopped people from becoming Bronies. MLP was no longer for kids!
Season 3: Babs Seed's awesome music video song. And Sleepless In Ponyville. And of course the line "That's because she is a Princess."
Season 4: Maud. The Pony Tones. And the Twilight vs Tirek DBZ battle.
Season 5: Lyra and Bonbon bumping butts. "'Cause the ultimate reward is a cutie mark!". Rara. Luna being vulnerable dreaming about sheep. Starlight Glimmer OP bada*s facial expressions.
Season 6: Rainbow Dash being relatable and Stranger Than Fan Fiction. Twilight sweep game. Spike getting a good episode.... No two episodes!
Season 7: Rock Solid Friendship! A Royal Problem! Discordant Harmony! The Perfect Pear! Fame and Misfortune!
Season 8: Only one, but it stands out: Kirin!
Season 9: Top episode for me, of all seasons: Frenemies!