Hulk matches his strength. Thor is pure magic and that's Superman's other weakness. Scarlet Witch could mess him up badly. Vision if the Infinity Stone is magic and especially if he has Thor's hammer. But if Captain America can pick up Thor's hammer, Supes could, too.
But movie Supes hasn't been shown to have a weakness to magic, so maybe nobody.
EDIT: just noticed we're talking comics. Anyone magic or who can create kryptonite. Hulk is as strong as him (or maybe stronger now after he beat Sentry), but no one else is going to provide a physical threat.
Wait, i think there's an entire Avengers team with Superman-level giys now. Blue Marvel, Hyperion, Gladiator, Starbrand, and others.
Superman at his most ludicrously powerful (movies or comics) isn't being matched by anyone. They just had a superboy character with ludicrous-Supes power levels and he was so strong that he punched reality into pieces. Seriously, shattered it. With punches. Shattered it like a laptop screen in front of a writer, desperately behind on a deadline, with no good ideas coming to him.