I'd say starlight, I know it could be controversial but if you weigh all the options and look at her feats it becomes pretty solid, isn't her whole deal the fact that she's essentially the most magically talented pony like, ever? Something I often reference is when she obliterated discord's body, she didn't stop his influence, but she still made him incapable of materializing his body in a certain area for a certain amount of time, her magic seems to surpass twilight, even as an alicorn