For you to say such a thing when ponies like Fleur-de-Lis, Celestia and Luna exist, you truly have proven your dedication to the lady Rarity. Good on you, sir.
Why, there can only be one butt for me, my dear fellow.
Only the most shapely butt of the fair lady Rarity can fill my heart with joy! Every other butt is a mere shadow compared to her bottomy flawlessness, i say!
I don't think I could ever settle for only one butt when there are so many quality butts out there, but again, your devotion to Rarity is inspiring. And hey, it's definitely the marshmallowiest in all the kingdom.