FrothByte
Nailcutter Massacre
Ok let's put some proper thought into this. If Superman fought each of these opponents individually then here is how it will go:
vs. IM - Tony gets torn apart
vs. Hulk - Hulk becomes a punching bag. Hulk has trouble enough landing hits on Thor, as long as Superman utilizes his superspeed then he should have no issues dodging Hulk's blows. It will take some time to knock Hulk out considering how tough Hulk is, but eventually it will happen.
vs. Scarlet Witch - if Superman hits her before she gets her shields up the gets splattered. If she does get her shields up then she survives for a few seconds. Maybe her TK is strong enough to throw Superman around a bit, maybe not. If she can touch him with telepathy that could really mess him up, problem is I don't see how that can happen with her shields up. Eventually her shields will fail and she gets splattered.
vs. Thor - Thor will put up his lightning aura and that will zap Superman everytime he gets near. Doesn't matter if Superman can bullrush Thor before he gets it up, fact is Thor isn't going to get KO'd with one hit so we know he'll have a chance to surround himself with lightning. After that then everytime Superman hits Thor he also gets zapped in return. It will then boil down to which hits harder: Superman's punches or Thor's auto-lightning. Of course if Superman is smart he can just lazer eye Thor, but to do that he'll need to hold still which will allow Thor to retaliate with more concentrated lightning.
vs. Vision - Vision will go intangible and all of Superman's speed will be for naught. Then it becomes a stalemate and ends up being a contest of attrition. If you ask me, I think Superman gets tired of his superspeed first before the android powered by an infinity stone gets tired of being intangible.
Now, that's IF they decide to fight solo. If they work together, then every time Superman tries to take out one of the heavy hitters it means he'll give the others time to either attack or strategize. To be honest, I don't think any of the Avengers has the firepower to take Superman out, at least not without repeatedly bombarding him. Their best chance is to try and catch him and hold him down while SW puts him in a telepathic fugue.
Either that, or get him still long enough for Vision to plunge his hand through his brain.
So I think the Avengers have a chance at winning but only if they fight together. If they don't, then Vision probably ends up alone in a stalemate that lasts for a whole day or two until Superman gets tired.