I totally have to say Discord! While he may not be a true villain, he just had this aura of undeniable swag that said "Hey, I could take over the world with a snap of my fingers...but I'll just screw with you for the hell of it." I can't deny that Queen Chrysalis was pretty awesome though. Even though I hated that she just wanted to take Shining Armor so Cadence couldn't have him, even though she didn't love him, I can't deny that her motives to feed her people were justified.