Who would win in a fight between Superman and Thanos?
Have to agree with the other guy. Who should win? Logically Thanos. Who will win? Superman because DC would never have it any other way. With the Infinity Gauntlet even the most blinkered DC fan would have to admit Thanos would simply erase him from existince.
Without it though Thanos should still win. Superman has greater strength but I would argue Thanos has the greater durability. Particularly to energy attacks. He tanked a point blank scream from Black Bolt with only slight blood from his mouth and laughed at the full might of Thors magical lighting striking him. Would the current version of Superman have fared so well? Maybe not. And this is if he allows himself to be struck. His forcefields are famously impenetrable and were even complemented by Galactus.
Thanos own energy bolts can shatter planets and staggered Galactus (If anyone says Superman can beat Galactus we will have a disagreement) and Supermans heat vision would not harm him as he is also ridiculously resistant to heat. He can move and react just as fast as Superman. He can also use matter and energy control on a Universal scale. I don't think he could use his matter manipulation to alter Superman's physique, but he could surely drain the solar radiation from his body rendering him mortal or radiate red sun radiation to have an even greater effect.
If this wasn't enough Thanos has psionic powers on a par with the best earth has to offer, enough even to disturb Galactus (again) He also has access to powerful magic, and although it is not his strongest suit is another form of attack Superman has shown some vulnerability to.
Thanos has humbled the strongest line ups of earth's mightiest heroes with embarrassing ease on his own, without any enhancement. Wheras Superman struggled with Thor alone, it could have gone either way. If properly written Thanos could KILL Superman. But as he always has to lose he would probably leave the ultimate nulifier lying around while gloating in victory so Superman could win.