I feel like this question needs context as well. What is the context of 'powerful'? If you are talking about direct combat then I wouldn't put AonDor near the top because they still have to use precious moments to write the Aon they need unless the have the preparedness necessary to have inscribed Aons that have any modifiers they may need on their person whereas a Mistborn, Feruchemist, or Surgebinder just needs to have their metal/sheres ready and can use their magic pretty simply. Now if you are talking about fortifications, preparedness, infrastructure I would very much say that AonDor is the most powerful.