@VinMcCarthy I gotta go with my personal favorite out of all of Erza's numerous armors - the Black Wing armor.
Erza gains the ability to fly with this armor, not unlike some of the others such as Heavens Wheel, but this armor also increases her offensive capabilities and also allows her to wield any of the various weapons she has to deal a great blow to her foe.
The armor also has the unique spell called Moon Slash in which she bull rushes the enemy to slash in a cross pattern to deal heavy damage. Personally, I just find this armor really cool because her wings are similar to those of dragons and the markings of the crosses and how the armor uses essentially shields as leg guards is an intriguing idea to me. Don't know why but it is o.o