I have to disagree and say Magneto.
Hal even as Parralax is still bound to flesh. Thus Magneto could manipulate the neutrons and iron in his blood to keep him from being able to do much of anything and cause his head to explode nigh-instanously.
And considering Parralax isn't a mutant Magneto would have no rancors. Assuming Maneto KNEW he wasn't a mutant cause if otherwise I hope Hal kills the bastard. Save us three pages of political dialogue lol..