Followed by Pinkie Pie for her sugary diet and Applejack for all the exercise she gets applebucking. Twilight has a big ass from sitting on hers all day as well as a benefit from her alicorn ascension. Fluttershy would be normal (with big crotchboobs). Rainbow and Luna would be the smallest. My favorite of course is Rarity’s marshmallow butt.
For me it’s the opposite