Ok so lots of people seem to think that Rarity and Fluttershy are best friends because of Green Isn't Your Color, and I agree, they do seem to have a close relationship. But I think Rarity and Pinkie Pie's friendship is a bit stronger. I mean, think about it. How many times have you seen Rarity and Pinkie standing together in an episode? That isn't the only thing. Pinkie Pie said "Rarity catch me" as she jumped of the wagon in The Last Roundup, which shows that she trusts Rarity more than everyone else. Also, they were seen standing up for each other in Putting Your Hoof Down, and they were together throughout the whole episode. And more recently, in The Gift of Maud Pie, they formed a special tradition together! If that's not a close friendship, I don't know what is! And it's not just in Equestria! In one of the Mini Clips for Rainbow Rocks, there was a song called Perfect Day for Fun, and Rarity and Pinkie were shown at the carnival together.
Just a thought, but what do you guys think is the reason that they seem so close?