How would you measure "power"? And more importantly, why would you want to know?

Grindelwald and Voldemort were strong in magic. Gellert could non-verbally parry a spell with ease (as Percival Graves), and Riddle's horcrux idea was fairly successful.

Ummmmm witch is probably Professor McGonagel (sorry I have no idea how u spell that) or Dumbledoor's mother

Wizard is Voldemort, or Dumbledoor's father

But how do u measure power?! It's really a mater if opinion

I think the most powerful wizard/ witch isn’t the one who knows all the spells and has won many battles. The most powerful wizard/witch is one who shows courage bravery kindness and is thoughtful. He/she has to show that they belong in this world. So yes most will pick Harry Potter or Dumbledore but in reality the one who should win is Neville or Ron. Neville stood up to Voldemort and used his friendship with the others to do so. Ron most of the time seemed like he was scared but in the end he was one of the bravest wizards out there. Now witches this would be Hermione or Ginny. They both showed how brave they were and that just because they were girls didn’t mean that they weren’t brave enough to be in the battles that the others were in.