Starlight's mane change is the worst. Her mane is not anatomically correct because it's not aligned. The only one I like is the CMC getting cutie marks, but I wish my favorite character got a permanent change so I voted other.
Wait...Starlight's mane changed?
Surely I can't be the only one who didn't notice...right?!
None. Mine hasn't happened yet and I'm not sure if it'll ever happened. I stopped watching after mid-seasons 6 because of all the unfairness, but if a change I'd favor or the creators pulled themselves to make the show fair. then I'd be back in a heartbeat.
And of course, Starlight is much prettier with the new do!
Starlight's mane, without a doubt. It's such a subtle change, just the bangs actually, but it signifies a change in the character of much greater proportion and I think the way it immediately brings it across to the viewer is an impressive bit of Art.
CMC: A great turning point for them that opened up new paths. They're not being treated more like adults even though they act like it a lot of the time so while great, it lacked impact.
Changelings: I very much approved of their looks while others gawked in disapproval so I have more support there. However, it was a cosmetic and attitude change that has contributed to world building but was not ground breaking.
Starlight's Mane: A minor cosmetic change that has significance but hasn't been used for much than a quick reference in another episode.
Spike's Wings: A most recent change that gives him some more help as a character in interacting but the effects of such are yet to be seen in great regard.
Other does not apply.
Twilight's wings: Though controversial at first, these wings opened up Twilight's path as an alicorn and opened up the series to the world building that appears more often. No longer were the Mane 6 friends learning lessons but from that point on, they became regarded as heros/heroines publicly, called upon for advice, and sent out on missions to help the world. That turning stone opened up avenues for all the Mane 6 and lessons that were beyond reach beforehand. This, with it's impact, is then the greatest change made in the show.
CMC - It was an over of a long chapter in their life. That plot was going on for six seasons, definitely very satisfying transformation.
Twilight - This one caused a lot of controversy in the fandom. I didn't like it at first, but learned to like it overtime.
Mane - Frankly, I don't give a crap about how someone changes their hair. Compared to the other transformations, which were life-changing, this is a minor one. Many things could go in here, and it probably deserves larger percentage than it has.
Changelings - Similar to Twilight's transformation - didn't like it at first, but got used to it. I like how their kind is so characteristic and unique,. (all species in MLP are)
Other - I believe this means reformations like NMM/Luna or Discord. I liked Luna's a lot, Discord's... not so much. He had better impression on me as a villain. I believe that "other" category could include weddings, since it's about as life-changing as getting cutie marks.
Spike - Here comes my favourite one, just barely edging the CMC trio. Spike was one of the main characters since the start of the series (although I think we have less of him nowadays) and this was absolutely deserved. Similarly to the CMC, He had to go through trouble to achieve it, and it caused no controversy. Here comes my vote.
I choose Starlight's Mane =3