Stipulations - This is a pure hand to hand slug fest. Thor does not posses Mjolnir and cannot use his other powers. Superman does not posses his other powers such as flight, heat vision etc. It's all strength, durability, endurance and so on. Also, just to make things more effective, let's say they each posses the same level of speed, somewhere in Quicksilver's vicinity and the same experience.
What has Superman done, that clearly places him above Thor in strength?
It's not like Thor is capable of planet shattering blows, resisting the weight of half the planet and even resisting the weight of multiple planets, overpowering and lifting the Midgard Serpent or anything....
Giving Thor Mjolnir in such a situation would practically be spite. By the way, Mjolnir doesn't increase Thor's physical strength.
thor would barring a warrior madness beat down, thor can and would rely more on his thousands of yrs of combat, he would be more likely to land the killer blow. thor does not have any moral reason to hold back in battle a neck snap ends supes DC's reign.
so with all things being equal what your really asking is whose spirit is stronger. that i'm not sure since both have fought to the bitter end several times. i'm more inclined to say superman if he was fighting for anything. In a friendly battle then it's thor because for thor every battle is very serous even if he doesn't kill the other person.
So.. since they have the same experience as well here is this thread just about comparing physical atributes such as strength and durability plus their natural willpower?