This is a tough topic to post on...In my heart I love Cadence, and Luna. I will never choose between them! Luna is so graceful and her character is drawn so perfectly! Cadence has that AMAZING singing voice and is just so beautiful when her hair is unkempt. Celestia is next after them for the depth of her character and the prominence she has within the show. I'm still on the fence about Twilight being a princess, the process didn't quite feel right but at the same time I'm happy she is progressing after so much effort.
So
Cadence/Luna
Celestia
Twilight