I love them all equally. To pick one over the other would be like your organs saying one is more important than the other when in reality if you lost even one you would die.
So since we all have organs if one of us loses an organ we all die and since we all watch ponies if we pick favorites we all die.
Oh yea, my favorite is pinkie/twilight/luna/rarity/fluttershy but not in that order.
But Luna is the best pony.