Sassy Saddles

I like how the show has developed supporting characters for each of the Mane Six over the years, but perhaps none have made as many new friends and contacts as Rarity has.  Her adventures have introduced us to Hoity Toity, Sapphire Shores, Fancy Pants, Coco Pommel, Saffron Marsala, Coriander Cumin, Plaid Stripes and her landlord father, Prim Hemline, Blueblood, Jet Set, Upper Crust, Zesty Gourmand, Suri Polomare and plenty more.  Added to her little sister and her parents, it's quite possibly the largest supporting cast and has gone a long way to fleshing out Equestria in general.

Unless you count Spike, she's also the only member of the Mane Six to have employees.  Sassy up there was an interesting addition to the Canterlot cast, starting as something of an antagonist within Rarity's own boutique.  I was a bit surprised to see her and the Canterlot branch of Rarity's business staying beyond her main episode, and she quickly made a reappearance in "Rarity Investigates" much to my delight.

I find these alicorn-body-styled unicorns to be intriguing as well...  The show is definitely branching out into other pony bodies as it goes on, but these still stand out to me as being just shy of actual alicorns rather than just slender ponies.  To my knowledge, we've never seen the body type used for a Pegasus or Earth Pony, which is interesting... although I don't know that it means anything at all.