With any fictional characters, and especially with superheroes the answer is "Whomever the current writer WANTS to be the most powerful." Power levels fluctuate to the needs of the story at the moment.
Based on what we've seen in the MCU, I think you'd have to say Captain Marvel. Thor, after his powerup in Ragnarok is pretty dang powerful, but Carol ripped through a Kree battleship like it was tissue paper. We haven't seen Thor do anything quite that bonkers yet, and Thor beat Hulk in Ragnarok even before his powerup was complete. Though we haven't seen Thor with Stormbreaker for very long, so who knows?
In the comics, my knowledge is a bit dated. I understand Thor has the Odinforce now, and is pretty powerful. However, Carol is also an energy absorber in the comics, something we don't see in her movie. She has absorbed the power of a star to go into 'Binary' mode, and in Binary mode she's bonkers powerful too. And Hulk of course gets stronger as he gets angrier, something I don't think has ever explicitly been stated in the MCU. I don't really know how to choose there. I think I'd go with Thor because his Odinforce is more predictable than Hulk or CM's strengths.