Well this two characters share something in common and that would be a source near to omnipotent power that they represent. Theorically Magneto & Dr Strange hold unlimited power limited by their human limits. By the side of science some one who can create & manipulate magnetism means also some one who can brake & shape the universe as he sees fit but with magic theorically you could do the same without reasonable explanation.
I will go with Magneto instead of Dtrange due the following reasoning.
God create the Universe and all the reality that exist & dont. All that can be seen & unseen . Is stated in the holly book that everything thas has to do with magic unplease God. Everything that the science can explain by physics is the way God allow anything to be.
So who will win.
Someone who wields a universal force that is accepted to be by God (not saying HE accepts that some holds such force) or source of energy that is allowed to exist but not graced at the eyes of God.
Magneto's best bet would be a quick draw scenario in which he quickly overwhelmed Strange's decidedly human level reflexes and durability before Strange augmented them or cast a simple spell on Erik. Generic mystical energy blasts and what not, I assume Magneto can defend against. Something like the Crimson Bands of Cytorrak or sending him to another dimension or attacking his spirit directly...I highly doubt it.
Obviously, feat for feat, this is spite against Magneto to the nth degree.
I'd give strange the majority with mags stealing a couple of battles due to strange human like relfexes. If Strange is ready for mags, Strange wins all the time. too many options.
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