Ground zero because it needs timing and it is super powerful.
Energy Ball for Fradz because it is underused I think, but REALLY powerful. If Fradz is alone you can get this spell to hit for full damage 3-4 times in one cast. That is crazy damage. Also it gives you temporary survival to get through impossible boss events with the right timing. And it's also a heal! Too powerful
Glacial ball because it is different. Cast time and a nice animation, plus you can make it deal twice the damage if you can walk an enemy with it.
Thats my vote!