Hoid
He is a former Dawnshard, giving him near perfect immortality, a lot of fortune, and a healing factor so strong even activly supressed he will heal a tooth in three days and shardblades mean nothing to him. Even Nightblood is only "possibly" able to kill him.
He is a Yolish Lightweaver and a Radiant Lightweaver, something Brandon says is "very dangerous" unto itself.
He is a Lersaium Mistborn, and probably a fullborn
He might have mikrokinesis
He has a lot of breath
Add to that his near endless political power, the fact that if he really wanted he could probably get his Dawnshard back, and the fact that he has a lot of items Brandon himself says he shouldn't and he is by far the most powerful non-shard in the cosmere.
No one else can really compare