For me I had joined the fandom in summer of 2013, so after Season 3 but either right when or right after Equestria Girls came out. I had watched it and I loved Season 3 the most, especially Magical Mystery Cure, because Twilight became a princess, there were amazing songs, great storyline, and an awesome finale to S3. I feel like the peak of MLP is from late Season 4-present, because we're getting so many great episodes!