Im gonna say it now there are manga spoilers in this before I start. Ok so I have made a list of who I think are the ten most powerful characters in the series are. Also this goes by every characters strength in their prime and without external help like deku using 100% with Eri's rewind to stop him injuring himself and overhaul's fusions because he needs somebody else to use them. Here is the list.
1:All might. All might obviously gets first place because even after sustaining major injuries he was still widely regarded as the worlds most powerful person.
2:All for One. All for one is the most powerful villain in the series so far and is basically immortal, however all might beat him so he gets second place.
3:Gigantomachia. Gigantomachia has only recently made an appearance in the manga and he is able to easily defeat the league of villains vanguard action squad and is has an infinite amount of stamina as he is able to stay up for a month and a half.
4:Endeavour. Endeavour is the current number 1 hero and he is shown to be extremely powerful and has great mastery over his quirk as he is able to generate white hot flames. Also he technically is more powerful than high end because high end was regenerating the whole time and endeavours prominence burn was able to incinerate him so since high end healed all damage he received and was killed by a single prominence burn endeavour one shot high end.
5:All Nomu. I didn't want to fill the list up with nomu so I put them all together. There are weak nomu that other weaker characters can defeat but there are also stronger nomu however they could be defeated by any of the characters higher up on the list.
6:Mirio(best boy) Togata: Mirio is shown to be extremely powerful as he was able to easily defeat most of class 1a and is able strong enough to break through concrete as shown when he breaks through overhauls spikes. Furthermore his quirk makes him immune to most attacks due to his high level of skill with it.
7:Gran Torino (in his prime): In his prime Gran Torino was able to move faster than young all might and was able to restrain him as well. Even as an elderly man he has been shown to be strong enough to shatter concrete with brute force and carry all might in his muscle form.
8:Overhaul. Overhaul is extremely powerful and is fast enough to easily evade attacks from izuku using 20% full cowl and his quirk is extremely powerful, however his greatest weapon is his ability to fuse to increase his power.
9:Hawks. Hawks is the number three hero and he is shown to be one of the fastest characters In the entire series. His feathers are able to carry people and are able to pierce high end.
10:Best jeanist/edgeshot. Neither Best jeanist and edgeshot are combat types however their ability to restrain their opponents makes them extremely powerful. They both seem evenly matched so I say they are tied in tength place.
Let me know if you agree with this list.