As my name implies I am a big fan of Doom so I am gonna have to say Doom wins this one. As for the mention of Magneto's forcefield being stronger than Dooms, keep in mind Doom's force field has withstood a subatomic blast in Secret Wars( I know this is a one shot). Also what is keeping Doom from just stealing Magneto's powers he has stolen many peoples powers in the past, not the least of which, Silver Surfer.
This fight basically boils down to how much preptime each side has. The more preptime, the more Doom's chances of victory are.
I give this to Magneto, however, for a couple reasons:
-Raw power. Magneto could destroy the planet on his own, without technological aid. He can also control almost anything that Doom tries to use, except magic ( by the way, Doom is NOT a master mage, YET. . . )
-Intelligence. Doom is tops, but Magneto is damned close.
-Tech. Doom has more tech, generally, but Magneto has access to as good of tech, AND has the ability to assemble it with incredible speed, unaided.
-Motivation. Dooms is motivated by powerlust and pride. Magneto is motivated by a cause, in which he fully believes. This belief in something more than himself will give Magneto the edge in this fight.
PS: But I wouldn't be surprised if Doom took this one 😉
Magneto has always been portrayed as Dooms ass-boy. He punked his ass constantly in X-Men vs F4. Doom certainly has a contingency plan for Magneto, magneto and him r "friends". Doom has sapped the power of beings immensely more powerful than Magneto on the fly, as well as going toe to toe with numerous cosmics i.e. Adam Warlock, Terrax, Silver Surfer, Thanos, etc. How about Hyperstorm? the most powerful mutant ever. Doom's armor is immune to Magneto's powers otherwise Doom would have never treated him like his *****. Magneto isnt as smart as Doom or Reed...comparing his is ridiculous. He's not even as smart as T'Challa who removed his powers and kicked his ass...what do u think Doom would do to him, he can neutralize mutant's powers just as well.