Nice to see someone else liking one of the fourth-rank, non-fan-favourite background ponies (I shall explain my ranks later in a separate thread). I believe I've seen her more than twice. Did you count the scene at the Summer Sun Celebration fair where she's about to nom a cupcake? As for me, I like so many background ponies that it's somewhat hard to pick a single favourite. But if I were to name one particular pony, it'd be Seafoam. (The unicorn with the two dolphins as her cutie mark, in case you don't know.) She's got the same mane and tail style as Colgate who is cute without a doubt, but her colours make her somewhat... je ne sais quoi. While she does appear in most episodes, often even in the foreground, she doesn't really stand out, probably also because people tend to confuse her with Sparkler. Her number of dialogue lines is the same as Ditzy Doo's or Colgate's, in fact, it's the same line—she's one of the three muffin girls. That said, I like unicorns in general, especially the six main background unicorns, and I hope that Lemon Hearts gets a more positive line in season 2 (and that the animators quit switching her eye shape). Of the unicorns, Sparkler would be my second favourite, closely followed by her own colour swap Diamond Mint. The other ones aren't too far down the list either. Very special mention: Vinyl Scratch. Among the earth ponies, to give the other kinds of ponies a chance, too, my favourite is Rose. She's a beauty, you should see her fan art, she has got both speaking lines and a blind bag pony of her own, and unlike her friend Daisy, she's not all over the place. Special mentions in this category: The Spa Ponies, Lotus and Aloe. Hope we'll see Frou-Frou in season 2 with her real mane style. Apple Cobbler is my favourite member of the Apple Family. Applejack doesn't introduce her to Twilight Sparkle, Pinkie Pie kicks her square in the face, so she does deserve some attention. Plus, she's cute. Maxie because there might be a brony showing up all over the Grand Galloping Gala. Last but not least, the mysterious blank flank Petunia. Now let's have a look at the pegasi. How about that golden-haired funmaker Cloud Kicker? There used to be times when she was mixed up with Ditzy Doo, but now she's on her way to the third rank—that of fan favourites—herself. She's somehow for pegasi what Lyra is for unicorns. Right after her at almost no distance comes Rainbow Day, the only fourth-rank pony to make it onto the SDCC poster. It was her who both suggested Rarity enter the Best Young Flyers' Competition (we know she's a professional weather maker since then) and mentioned Ditzy Doo's name. Ditzy herself is running outside the competition, of course, so a special mention goes out to her.
Like almost everypony I love the most Derpy Hooves, Lyra and Bon Bon. And that I'm not original is another reason to hate myself (but it does not mean that I do not want to like Derpy, Lyra and Bon Bon of course).
Really? No Vinyl Scratch lovin here? Oh well, Vinyl is mah favorite. I love that My Little Pony has a DJ pony! Sickness!!