Forgefiend Autocannons or Ectoplasma

So i am gonna be getting a Forgefiend soon and i cant decide if i want to attempt to magnetize the model that way i can swap things out or if i want to just set it up and leave it that way. All of my models to date are not magnetized as i well havent quite got up the nerve to try and do it. Part of me wishes that i could have an ectoplasma cannon and a hades autocannon (and yes i know i can take the head option but i want the head to stay a head not a gun) so which do you guys think is better, if you only had to pick one of the options?