All 6 are pretty awesome in their own way, really. Because I had to pick one, I edged out Twilight Sparkle due to having quite a little bit more intellectual integrity to the character. Rainbow Dash was tempting, but I had to pass on the grounds that she's a bit overly brash. Pinkie Pie and Fluttershy definitely possess their individual appeal. Rarity-centric episodes (Suited For Success, Diamond Dogs) go far in bolstering her appeal - Rarity meltdowns are surely the best: "I don't even know what I'm supposed to be wallowing in~~!". Apple Jack would be my #6 on the grounds she's just a simple country gal, but it's hard to malign a true blue workpony.