Ability Strength mods affect the damage of Pull, Polarize and Crush. All the damage that can be inflicted with Magnetize is also increased by these mods. They also affects the amount of armor reduced during Polarize and the amount of shields restored by Polarize and Crush. Ability Range mods will increase the range of Pull, the radius of Magnetize’s magnetic field and explosion, the initial radius of Polarize and the range of Crush. Ability Duration mods increase the duration of the Magnetize’s field. They also affect how long Polarize expands for.
So, all things considered, here are some builds you may want to try on your Mag: