Superboy (Kal-El)
While Kon-El’s relationship with Superman started with no conflict whatsoever, meeting the young Kal-El (an alternate universe Superboy) was a different story. A VERY different story.
Both Superboys would meet up in Smallville, where the events of Zero Hour had elements of Pre-Crisis Kal-El's world would phase in and out with Kon-El's world. And when Hero A meets Hero B, a fight will happen most of the time. Both Superboys fought with their respective powers, but cooler heads prevailed at the Kent Farm where they noticed the situation and talked.
Pretty much a "passing of the torch" from Kal to Kon.
They would eventually meet again. And this time, it was a definitely a brotherly bond between the two.