So this list of characters who could beat IG Thanos is just...bad. Sure, Strange, Hulk, Shazam, and Darkseid are incredibly powerful characters, but they are not at all on the same level. Shazam and Hulk are around Superman's level (see picture above). Dr. Strange is a bit better, and he could probably have a good fight with standard Thanos, but the IG gauntlet is insanely powerful.
The Infinity Stones, singularities that have been around since before the creation of the Universe (or something) include the Mind, Power, Time, Reality, Soul, and Space gems. They are crazy powerful, and when put together and amplified by the Infinity Gauntlet, they are even more powerful. In fact, the wearer (if powerful enough to wield them without being consumed) becomes a pretty high-level reality warper, capable of literally changing the universe at will.
It's a nice thought that someone who basically punches things, like Hulk, could possibly beat someone who could actually just wish Hulk to the other side of the universe, but of course that's not really possible. Even Shazam and Dr. Strange, who have many more powers than basically just punching things, are no match for Thanos with the Infinity Gauntlet.
Darkseid is on another level. Unfortunately, Darkseid is also a DC character, not Marvel, so the comparison is a bit harder to make, but the contempt with which he puts down Superman ought to give you an idea of his power. Darkseid is the ruler and effective God of a planet called Apokolips. His Omega Beams are one of the most powerful weapons in the Universe. His abilities also include telepathy, telekinesis, teleportation, size alteration, incredible physical strength, insanely high durability, and immortality. He has access to some pretty ridiculous weapons, like the Promethean Giant:
So basically, of these four, Darkseid has the best chance of actually beating Thanos. Here's some other characters who might have a chance of beating IG Thanos: Odin (the Allfather, wielder of the Odinforce), Death (yep, the universal entity), Eternity (the personification of eternity, I guess) the Beyonder, and Franklin Richards (look him up, it's insane).