In theory AFO as he is now should be the strongest we have seen. Shigaraki's body isn't in great condition but it's still a body that at base has physical strength in the realm of a full powered OFA user. On top of that you have AFO and AFO's mind in control without interference from the shigaraki persona or tenko. Shigaraki was of course a skilled fighter, before getting AFO he was up there with top heroes in terms of skill alone. But there's no reason to think any hero or villain around ever came close to AFO (or allmight) in terms of skill alone. The saving grace of this angle of the plot is that shigaraki's body is not in good condition and there's an army of heroes willing to face AFO. I wouldn't be surprised if some of the more cowardly heroes who retired earlier also show up. I suppose that for the theme's sake what will win the day is ultimately deku reaching out to the depths of AFO and finding/freeing the tenko persona.