Why these two? because Superman vs Goku has beed done to death and there is the argument that Goku, while arguably as powerful as Superman, is inherently too naive/stupid for winning the battle (i don't think so, Goku has proved to be the best fighter of their universe despite that "flaw"). Meanwhile, both Gladiator and Vegeta are somewhat mature and intelligent enough for an even combat between them, IMO. And both seems to depend on their pride and self steem as fuel in battle. Consider both as their best incarnations and without intervention of the Shi’ar Empire, Dragonballs, other characters, etc.
Marvel's Gladiator:
Vegeta: