X-Men’s Colossus and the Avengers' Luke Cage settled which Marvel hero is stronger, a victory cemented by the winner killing the loser. Although not the strongest ever, both heroes have showcased events of great strength either in the protection of innocent lives or against any number of superpowered threats.
In one universe though, both Luke and Piotr are members of the Avengers who cross paths with the Exiles during their interdimensional travels throughout the multiverse. Although they fight on the same side, one of the Exiles convinces Colossus to switch sides, leading to a fight to the death. The Exiles are a group of mutant heroes from parallel worlds who are tasked with traveling to other dimensions and working together to fix them, either by preventing great catastrophes or allowing specific events to occur. This has led to a wide variety of alternate universes being introduced, such as one where the Exiles met a version of the Simpsons.
In Exiles #26 by Chuck Austen and Clayton Henry, they travel to a world where every major superpowered hero is financed by Heroes for Hire Inc, a business run by Danny Rand, Luke Cage, and Piotr Rasputin. When their refusal to intervene results in a villain causing a major disaster that kills millions in Japan, the Avengers are en route around the time the Exiles drop in. After learning the Avengers were meant to die, the Exiles are tasked with ensuring that they do die. While members of the Exiles choose to help the injured and dying victims in Japan, their leader, Illyana Rasputin, chooses to complete the mission. When the Avengers arrive in Japan, Magik gets their attention and then destroys their Quinjet, killing Black Widow. In Exiles #27, Illyana explains who she is and why she must kill all three of them, including her brother. When this fails, she is beaten and restrained by Iron Fist where she is to be killed by Luke Cage with Marvel's most powerful weapon, Magik's own Soulsword. She is saved by Colossus who has chosen to side with her and proceeds to kill Luke by driving his fist through his chest, killing the indestructible hero.
The process that gave Luke Cage his powers not only gave him superhuman strength and durability but also gave him nigh invulnerability which allow him to survive attacks from most conventional weapons and superhuman foes alike. Cage's strength can be comparable to Hulk, for reference. Colossus’ mutant ability to transform also allows him superhuman strength, durability, and nigh invulnerability but only within his armored form. Both heroes’ powers have allowed them to fight villains ranging from the Juggernaut to Doctor Doom and still live to tell the tale. While this version of Piotr’s powers is like his mainstream counterpart, this Luke Cage is noticeably weaker as Colossus can punch and impale him with little to no resistance. He also does not appear to have the same healing factor as well as he dies shortly after, shocked his killer is his teammate and close friend.
Although Colossus's strength is victorious over Luke Cage, his victory is short-lived as he has chosen to help his extradimensional sister accomplish his mission, the death of the Avengers with his body included. Although these were versions of both characters from another dimension altogether, one of the many missions the Exiles had to make difficult decisions for the fate of a world, one can only imagine if Colossus and Luke Cage ever did fight, who would be victorious, indeed.