New characters featured this season from best to worst, based on my personal enjoyment:

Party Favor true form ID S5E2

Party Favor - I just love everything about this pony. His design and his colour scheme are to die for. What I found interesting about him is that he never used his magic once in the entire episode. Maybe he never learned to use it, or he doesn't need it? Speculate away!

Starlight Glimmer - Although I hate her name because it's boring, her character is fascinating. Nuff said.

Moon Dancer - A great callback to Season 1 and a nice new character to make Twilight more 3D.

Sassy Saddles - She's simply marvelous, darling! (I love her various sayings).

Night Gider - Although she's basically a discount Wonderbolt, I don't think I'm alone when I say I love her design and colour scheme too. I hope she's featured in another episode along the road, perhaps for a Wonderbolt race or something?

Tree Hugger - Like Maud Pie, Tree Hugger is one of those characters who is either horribly bland or really amazing depending on the way you look at her. I hope we see more hippie ponies soon!

Double Diamond - I like his character because he seemed to have a long history with Starlight Glimmer. It took me a while to like his colour scheme, but I like it now.

Sugar Belle - I found Sugar Belle a little boring at first because of her voice, and her design was similar to and overshadowed by Party Favor, but she's cute I guess.

Windrider - A good addition (or former addition) to the Wonderbolts lore.

Trouble Shoes Clyde - His design was a bit bland to me, but that's only because that kind of massive, patchy horse seems a little too realistic to what's on Earth. It's for a similar reason why I don't like Pipsqueak and I think Gaffer from the comics?