Are we seriously having a best pony debate using post count? REALLY?! I'll trust your opinions on headphones, but ponies? They have nothing to do with post count.
Also, there is no comparing Twilight Sparkle to Derpy. The amount of development they have is vastly different. Of the mane 6, Twilight is best pony.
I'm not so sure about background pony... Derpy is alright though :P