Yeah I'd say Scarlet Witch. Or Captain Marvel.

Wanda and carol as both of them did fight him and could’ve won. Thor too, he did manage to impale Thanos with Stormbreaker. Thanos would be dead if he had gone for the head.

I say it's between Wanda, Carol, Dr Strange, and Thor from infinity war before getting fat.

Yeah, it depends

If Thanos has no infinity stones, it would be Scarlet Witch or Captain Marvel because we saw how Captain Marvel was vulnerable to the Power Stone whereas Scarlet Witch could only be a challenge for Thanos when he didn't have the Infinity Stones. As in Infinity War, she was thrown away by Thanos just like a puppet. Though she was emotional at that time as she lost Vision.

But the most appropriate one is Thor. Because his Stormbreaker can absorb the power of all the Infinity Stones as shown in the end of Avengers: Infinity War. And also the death of Loki and Heimdall fueled the anger of Thor. Both in Infinity War he sought vengeance while in Endgame too he was oddly angry enough when Professor Hulk uttered his name.

So the most appropriate answer of Thanos with all infinity stones are THOR

Wanda, black bolt, and honestly, I think Quake could explode his heart in a blink.

Scarlet Witch could kill Thanos

Scarlet Witch and Captain Marvel