My strongest case is simple: Goku wins on demonstrated feats, not implied potential. Sure, the other side can point to Saitama's no-limits gag, and that's fair as a story device, but in a versus debate we compare what each fighter has actually shown. Goku has universe-scale clashes, Ultra Instinct reactions, instant transmission, and a deep bag of energy techniques and martial skill. Saitama hits really hard, but he hasn't shown counters to that kind of speed, precision, and versatility. So until Saitama proves more than a gag, Goku takes it.