This has always been a debate between comic book fans and to be honest, it's fair. Both Thor's and Superman's power levels have fluctuated over time. Thor has been shown to be helpless without Mjölnir in one case but in the other he was shown to be the same while his hammer was just used to enhance his powers.
Superman has also been seen juggling planets but was also punched by Batman and got a bleeding nose. So in short, we can't really see or decide who's the most powerful hero between the two. Superman is arguably as strong as a god while Thor is a god himself. I could go on listing strengths and weaknesses but I don't think I could do or say anything that others haven't said before.
So, who would win between an all out fight between Thor vs Superman? Well, I have to say, it would be Thor.
Now before my head is blown off by fans, let me say this. I love Superman, I even have a tattoo of the S shield. But that does not change one major fact: Thor can use magic, one of Superman's greatest weaknesses. Magic itself doesn't hurt Kryptonians but it also bypasses but it also bypasses the bioelectric aura that gives them their powers which means that they are as vulnerable to magical attacks as any other mortal. That is why Shazam/Captain Marvel is sometimes shown to be able to beat the [Man of Steel](movie:15593). Batman himself said in the Batman/Superman comic book that Superman would lose in a 1-on-1 match between the two. Thor is far more powerful than Captain Marvel is.
I don't want to use the Odinforce Thor, just the 'regular' one after Mjölnir was broken on Bor's head and got reforged by Doctor Strange. Thor became a bit more powerful even after losing the Odinforce and he still had the ability to summon lightning. Now, the origin of this lightning is the only reason I think Thor would win. I've heard fans say that Thor can't really summon magical lightning, he only makes regular ones so it won't hurt Superman. If we'd be talking about the Ultimate Universe, I would agree. There, Thor has been using his armor to give him the ability to ionize his environment and create storms. He affected the world around him but the storm itself was just a regular one. Ultimate Thor would definitely be beaten by Superman.
But this is the Canon Thor and I believe that he is a real god and he does use his magic and Godforce to create magical lightning. Mjölnir itself is incredibly powerful a weapon an it's clearly magical.
It could also come down to who's the better fighter. That is another reason I'm saying Thor is clearly the victor. He has been battling armies and monsters for thousands of years. Sure, he does lose from time to time in the comics, but mainly that is because they need to show that he is not invulnerable or unbeatable. Same with Superman. Sometimes the writers need to show that he is still beatable and not all powerful. So, when it comes to battle experience, Thor is clearly the better fighter.
That's 2-0 on Thor's side right now, both in fighting skills and exploitable weaknesses. We could go into speed and strength but that is just so inconsistent that there really isn't a usable base I could exploit. Sometimes they say Superman can fight at lightspeed but other times, he can't, he only has the ability to travel that fast. Then again, Thor can also fight at lightspeed with Mjölnir, according to some comics and databases, but I honestly haven't seen it before. So, again, what source to use? I went with Thor after his hammer was repaired and regular New 52 Superman. Comparing the two... I honestly can't decide. Both are incredibly powerful, fast and intelligent fighters.
The problem with both of these heroes is that they are not really independent characters, more like an organic power scale for other characters. If a new villain or hero arrives and they can hurt Thor or Superman, we instantly know that hey mean business. They are just used as tools to show others' power levels or to be deus ex machinas whenever the writer is in a corner and can't solve the problem they have written themselves into.
What I'm trying to say is that is it almost useless to compare the two, but if it was a fight between the two, I would say that Thor would win, only because of his experience in battle and the fact that he can use magic.