Warning! Spoilers ahead for Superman/Doomsday: Hunter/Prey #1!
Although Superman has a wide-ranging roster of villains that regularly hunt him, only a few are actually feared by Superman. Darkseid and Doomsday are two of those. Capable of seriously endangering Superman due to their raw power, Superman often struggles to defeat them without getting some serious backup or coming up with an ingenious plan.
The list of universe-threatening villains that have come for Superman's head is endless. Not every villain poses a physical threat in the way that Darkseid and Doomsday do, but there's no denying that they are the ultimate match for the Man of Steel. Not only are they Superman villains, but Darkseid and Doomsday are seen as two of the most deadly threats in the entire DC universe. They have been the cause of many crisis events and will be for many more.
Darkseid, created by Jack Kirby, first appeared in Superman's Pal Jimmy Olsen #134. Darkseid is the tyrannical ruler of Apokolips, a fiery hellscape of a planet. He is a god-like being whose villainy is endless as he's always planning his next attack on DC's Omniverse. Darkseid has an incredible set of powers that rival Superman's abilities. Darkseid can harness an enormous amount of energy and shoot out Omega beams from his eyes. Darkseid's Omega effect is much like Superman's heat vision, albeit completely overpowered. It has the ability to change directions and hone in on any target. Essentially, Darkseid can never miss. This is just one aspect of Darkseid that makes him extremely powerful. Darkseid's army is another thing that makes him all-powerful as he is the tyrannical ruler of an entire planet and his citizens obey him, no matter what.
On the other side, Doomsday is the ultimate killing machine and arguably, Superman's greatest threat. Created by Dan Jurgens, Doomsday first appeared in Superman: The Man of Steel #17. Doomsday is best known for his role in The Death of Superman where he kills Superman. This is the only time that Superman has died in the main DC universe, thus, Doomsday is the only villain to have bested the Man of Steel. The reason for his extreme brute force is that he was designed as a killing machine and nothing else. Doomsday's only purpose is to cause endless destruction as he demolishes everything in his path. Barring a few instances, Superman is barely able to do any damage to Doomsday, despite his best efforts.
In Superman/Doomsday: Hunter/Prey by Dan Jurgens, Brett Breeding, Bill Oakley, and Gregory Wright, Doomsday lands on Apokolips. The tables are instantly turned as both Superman villains, Darkseid and Doomsday, are forced to face off against each other. Doomsday's attack has nothing to do with Superman and their feud starts solely between Darkseid and Doomsday. Doomsday's one purpose in life is to kill and cause destruction. Therefore, as soon as the Superman villain arrives on Apokolips, he begins his next murderous rampage, causing chaos all over Apokolips. The issue reveals that even Darkseid fears Doomsday, thanks to his legend as a planet killer. Darkseid realizes the stakes at hand and knows that the only way for Apokolips to survive and be rid of Doomsday is for him to take on the beast himself.
Darkseid sets out to face Doomsday alone as he readies to let loose his Omega beams. As stated, Darkseid's Omega effect can blast out infinitely powerful beams of energy. No one has ever survived the Omega beams, especially not from point-blank range. Yet, Doomsday survives and approaches his attacker with fiery rage. Darkseid is stabbed in the back by Doomsday's claws, making the ruler of Apokolips bleed. At which, Darkseid exclaims "the legends... are true. You are... beyond death." It's clear from their battle that Doomsday is the ultimate world-ending threat of DC's universe, given that he is easily able to defeat and nearly kill Darkseid.
However, it must be noted that throughout history comic book villains vary in terms of power. If Darkseid were to take on Doomsday again in the Infinite Frontier era, it's possible that Darkseid would reign victorious. This is because Darkseid has been remade and reformed into the ultimate version of himself. Darkseid is aware of every past iteration of himself and has learned from his past mistakes. Additionally, somehow, Darkseid has been granted greater powers than he's ever had. In Infinite Frontier #0, Darkseid escapes from his confinement on Earth-Omega. and kills the Quintessence. Having such raw power to murder literal gods is a huge statement that proves that DC's universe is in big trouble.
It must not be forgotten that Darkseid is incredibly smart, whereas, Doomsday is just pure muscle. Currently, Darkseid can leave Earth-Omega and try his hand at destroying DC's new Omniverse. However, Darkseid has something greater planned which will ultimately be more effective than attacking right away. On the other hand, if Doomsday were to be in Darkseid's current position, he would have no thought process about anything like this. If both Darkseid and Doomsday were to battle in the fields of Infinite Frontier, Darkseid would have the upper hand.
Ultimately, Darkseid and Doomsday are much alike in terms of the level of threat. Superman would much rather fight any other villain than both of them. Although Doomsday was able to take down Darkseid easily, Superman could never. It's a fact that Darkseid isn't an easy threat to defeat. If Superman's powers ever achieved the heights of Doomsday then that would be a different story. But it's clear that DC Comics would never do that as Superman would be even more overpowered than he already is. Superman/Doomsday: Hunter/Prey highlights why Doomsday is the only villain who has ever killed Superman. It would be great fun to see the two Superman villains fight it out in DC's new era, given Darkseid's recent power-up. It's been teased that Darkseid's plans for the DC universe are unlike anything that has been done before. Perhaps, he will prove to be not only Superman's greatest villain but DC Comics' biggest threat of all time!