I'm obviously gonna say Moondancer. Everyone I know likes her! I admit, her pose may not be the greatest, but at least she's not afraid to wear fender thighs! XD I can relate to her there. Besides, Sunbeam's in that pose, too, so she should get equal blame.
Moondancer plays the quintessential part in all of us: the trickster! Laughing, carefree, and wild, she is what we all are deep down. Her pose always struck me as more graceful than the goose-stepping pose of Glory. Everyone I know seems to prefer Moondancer. I've had a 50 year old teacher tell me that she was absolutely crazy about her!
While Glory is what we think of all unicorns, Moondancer is playful and nutsy and exactly the opposite. She's different from other unicorns at the time, as she's less mystical in that sense and more of the Coyote from the trickster tales of the Southwest.
So while Glory is probably more conventional and classic and almost always gets nominated first, Moondancer is what we are inside, therefore making her, in my opinion, the quintessential pony. She has a different sort of beauty as well, a spirited beauty that those who understand her can see, while Glory's is more on the surface.
I'm done. XD