Most improved episodes.

[CastletonSnob 3,089]

Which character had the biggest improvement in episode quality as the show went on?

[abronymouse 6,144]

Other than the background ponies, whose voices and characters were pretty much fan inventions until later eps, I think Spike had the greatest improvement. It took until season 5, I think, for me to like his eps.

That speaks more to how bad his early eps were though.

 

[Thrond 3,271]

The Cutie Mark Crusaders started off as the characters whose episodes I dreaded in those first two seasons, and then grew on me as they became less obsessed with their cutie marks. I enjoyed most of their episodes from season 3 onwards, I would say. 

Starlight Glimmer actually repeated the pattern for me in the latter half of the series, where I had limited patience for her until season 8, when she became a bit more stable without just turning into off-brand Twilight.