When I first saw this topic I immediately thought Magneto wins easy.
But after thinking about each of their powers more, I think Iceman could beat Magneto.
They can manipulate each other at the molecular level.
Iceman can manipulate his own body at molecular level also.
To what degree can Magneto manipulate and control his own body?
If Iceman is Omega mutant there is no reason why he cannot be as powerful as Magneto, except for writers choosing him not to be