My power ranking would be:
8. Jack
I think we all can agree that when it comes to overall power, durability, speed and endurance he's easily the weakest fighter presented thus far. That doesn't mean though that he would be totally unable to win against some of the fighters ranked above him. His intelligence, trickery and cunningness make him able to have a decent shot at winning against some fighters ranked above him. The reason I ranked him in the last spot in the ranking is that, despite his Volund being really good (probably the most broken one so far), he can only show its full potential in an arena like the one he fought in against Hercules. If he fights in a straight arena like the one most of the battles thus far have taken place, I don't think he would be able to do nearly as well as he did. Not to mention his other stats aren't nearly as good as the other fighters'.
7. Lu Bu
One of the physically strongest humans, but sadly not much more. He's a straight fighter that depends mainly on physical strength and his fighting style is really straightforward and centred around overwhelming his opponents. I don't see him winning against any of the fighters ranked above him. Either because some of them are physically stronger, faster and/or have more skill and versatility.
6. Hercules
Immense physical strength and durability but that's not all there's to it. I rank him above Lu Bu because I think that when it comes to physical strength both are even, but Hercules has more versatility going on for him with his Labours.
5. Sasaki Kojiro
Both his adaptative capabilities and his evolution during battle are insane. I don't think any of the fighters ranked below him would be able to beat him in a straight fight. Hercules is way too linear, not to mention that Jack was able to react to his attacks so I don't doubt that Kojiro will be able to do it as well. Lu Bu is more of the same. Jack is the only one I can see winning against Sasaki due to his intelligence and cunningness but in a straight normal fight, Sasaki most likely wins too.
4. Thor
Probably second only to Odin in the Norse Pantheon. He beat Lu Bu handily, and his Mjolnir is probably the most dangerous weapon in this tournament. A single strike can pretty much obliterate you, its power and speed is off the charts and coupled with Thor's immense physical strength makes the weapon even more broken than what it is already.
3. Poseidon
Called the Zeus of the Seas. This position might be controversial here, but he wasn't portrayed as being much weaker than Zeus. He toyed the whole fight against Sasaki and let him adapt and evolve by increasing his power little by little. Had he fought seriously since the start instead of acting like the cocky little shit he was, the result would have been really different IMO. Not to mention, he easily disposed of one of his brothers, who was stated to be a really high-level deity too. I put him above Thor because his attacks seem to be much harder to dodge than Thor's, whose attacks seem to be pretty linear in comparison. He should be able to attack using water too, considering what he did in his entrance to the ring, but sadly we never saw any offensive attacks in that department, maybe because he underestimated Sasaki far too much.
2. Adam
Best daddy. His foresight is immensely broken. He was able to overwhelm Zeus with ease. He can even copy and react to techniques that stop the flow of time. Fought evenly with Zeus in his Adamas Form and had a good shot at winning. His durability is pretty damn great too as he was able to tank attacks from Zeus in his Final Form, who is probably the being with the highest physical strength showed thus far along with Thor and his hammer. The reason he's ranked second despite beating the shit out of Zeus during most of the fight is that his godly foresight puts a huge strain in his body and he's unable to use it permanently or for large periods of time, which is the reason why Zeus was able to beat him in the first place.
1. Zeus (Adamas Form)
Undisputably the strongest character so far IMO. He's incredibly fast, can stop time, use lightning (which for some reason didn't use in his fight against Adam) and his Adamas Form is even more broken and durable. He can maintain this form for around 13 minutes at full power. In his battle against Adam he was capable of beating him with only the 7 minutes he had access to due to his injuries. Honestly, I think the first two places of this ranking are interchangeable. Zeus can beat Adam if he goes into his Adamas Form but if Adam doesn't fuck around and he's able to finish him before he goes into that state then he wins. I'm giving Zeus the benefit of the doubt overall. Both fucked around during pretty much all the battle, but in the end, the one who won was Zeus.