Power wise I would say they are even. But, when looking at strength of character She-Ra beats He-Man hands down. There is just so much more to her story. She went through a great deal more trauma and hardship than He-Man, in order to find herself and her powers. She came from darkness into light. I read an artical a few years ago that was looking at a similar issue between Hercules and Xena.
The paragraph at the end the artical just spoke volumes to me about parallels that could be drawn to He-Man and She-Ra. Putting this text into the context of MOTU it would read something like this. He-Man is an example of the hero we all hope is out there, the saviour we all want to believe in!
She-Ra represents the hero we hope is within us all! One who makes the choices necessary to change their destany and find the strength within: to ultemately save them self!
I really don't like the question do I think She-Ra is better than He-Man. I prefer to look at it another way. When together they were just unbeatable!!!!!!!
Their abilities totally complemented each other. They were partners in battle, equals in every way. There was never a power struggle between the twins, so why do we have to create one?
Maybe the question should be Who is stronger than He-Man and She-Ra when they stand together?