June 12, 2014 6:03 PM EDT
this will probably be unpopular but I'd have to say the most overpowered build I've used in recent memory was a Destruction/Restoration mage. At one point I had to use console commands to remove the impact perk because it completely breaks the combat system and even then I still found it stupidly overpowered. And this was without using Conjuration or Illusion for a good chunk of the playthrough.
Paralysis, turn undead and impact give you field control that no other build can even come close to touching, as long as you have enough of a magicka reserve (I put everything into Magicka and had over 800 by the endgame, plus enchantments). If you then add in Conjuration and/or Illusion then there is literally nothing that should touch you, no need to even use stealth you can just waltz into any area and brush enemies aside with little effort.
The master Destruction spells are so horribly unbalanced that it's almost a crime, undead stand no chance against a master destruction mage and everything else may take 1-2 more casts before they're obliterated. Without using Conjuration/Illusion I think the Mage style is the most overpowered, if I also include those schools then there's not even a debate in my mind.