Sorry If I double post, I tried once and it said complete but now the post isn't here. In an identical environment which boss would pose a bigger threat? I personally believe that the damage of both bosses is nearly equivalent. That being said I believe the alien 2 boss is tough due to a few things....

Honestly I would have to say D2 final boss is tougher seeing as earth shakers disorient you and even if you are invulnerable it burns time either getting away when a power up is wearing off and when you are trying to aim. Sure D1 megas did more damage but I think the fact that they scaled them back ...