Of all the characters, I think Trixie has shown the most growth in the show.

No — seriously — see if you follow me.

She starts out a traveling entertainer, living in a caravan, going from town to town trying to drum up enough business to get to the next town. She visits Ponyville and leaves humiliated, embarrassed, homeless, and odds are without a bit to her name.

As the show progresses, she finds one of the rarest treasures of Pony Kind, and returns and wins her revenge over all of Ponyville — especially over her nemesis — and breaks the 4th wall so hard even Pinkie Pie is left speechless — but she learns it wasn't worth it. And, in the end, has the dignity to admit her mistakes, and the humility to join the celebration with the rest of the ponies.

Then despite the doubts and open opposition of many, she becomes the friend — the TRUE friend — of one of the most important and powerful ponies in all of history ( comic VERY related ), goes on to perform one of the most amazing life-daring magical feats ever attempted by Pony Kind. She travels the world with her new friend, puts Discord himself in his place, sacrifices herself to help save all of Equestria from the Bug Threat, and wins the adoration — and respect — of everyone.

And, in Fanon, Trixie saves her mother from an afterlife of haunting the world wrapped in chains, and brought to the world the wonder and joy of the Cake Hat.

Teacher, Sometimes Counselor, Transformational Magician, Mistress Of Teacups and Teapot Puppies, The Great And Powerful; Trixie Lulamoon.

From a fascinating but otherwise throwaway pony in a one-off episode, to one of the cornerstones of the entire series, she has always been, for me, Best Pony. And I think her character arch is one of the most interesting stories in the entire series.

ps: oh my god I haven't drawn for a whole year, why is drawing so hard!?
pps: oc:ghost is the creation of artist:evil-dec0y