Superman is seen as being synonymous with the highest level of power in the DC Universe; the list of characters able to defeat him in 1-v-1 combat is incredibly short.
Nonetheless, two figures that often occupy that list are Black Adam, and his heroic nemesis Shazam. This is because of their relatively similar power sets to Superman, but also due to the fact that their powers are based in magic – a commonly cited weakness of Superman. Certainly, especially considering his aggressive, relentless nature, Black Adam is among the top challengers for the title of Superman’s most worthy opponent.
However, if the off-hand remarks by Batman and Green Arrow in Justice League #73 are to be taken at face value, even DC’s heroes consider Superman to be unequivocally more powerful. In the issue, Black Adam has been possessed by an ancient Lord of Chaos named Xanadoth, who uses his body to wreak havoc upon the Justice League. This leads to a joint meeting between the main Justice League and their magic-based counterparts in the Justice League Dark, as they try to figure out how to counter this new threat.