Mane six human body types GO:

Twilight is "average sized", in terms of both height and weight.

Pinkie Pie is, of course, short and chubby; and being a trans woman, has some muscle.

Applejack is on the taller side and muscular.

Rainbow Dash is average height, if not on the shorter side.

Rarity is taller than Pinkie, but shorter than Twilight. Has a thick figure.

I don't care if this is over-used, I still imagine Fluttershy as tall, and has some pudge. She's really insecure about her body.

So in order from shortest to tallest: Pinkie Pie, Rainbow Dash, Rarity, Twilight, Applejack, and Fluttershy.

Oh yeah, and they've all got a nice ass.