Mana Loading is by far the best pick for anyone with a 30% battery. With it, she Black Grail loops easily. Without it, she doesn't. No other append will even have much of a value at all. If I had to rank the other ones I'd say 5>4>1>3.
Triple Skadi, double Skadi Castoria, double Skadi Oberon. If you don't have the support to do Black Grail, Mana Loading is still the best by far with a 50% CE for looping. I can't see any meaningful use for the other 4 appends, and Mana Loading will always be useful to anyone with a 30% battery.
