I gotta say it would be between Pinkie Pie and Twilight Sparkle, and of those two, it would probably be Pinkie. Rainbow and AJ would go after each other first, tiring themselves out, Fluttershy hides in the corner whimpering and the moment something dirty or bloody touches Rarity, she'll pass out on her couch. Then Pinkie, through the power of the fourth wall, will break Twilight's mind as she tries to figure out how Pinkie is breaking all laws of physics while being pummeled by whatever Pinkie pulls out of hammer-space.