Who has enough powerful magic.

I didn't quite understand the question, as in Heroes of Might and Magic V, there isn't the same division into magical schools as in Heroes of Might and Magic IV... but I'll try to answer:
In 1st place, naturally, due to the specialization in magic, Dark Elves will be stronger....
In 2nd place, Mages... it's a shame for them to be lower..
In 3rd place, Demons... and so on.