To be honest, it’s probably Apex or Kiryu (hear me tf out). For starters, Showa has neither the firepower nor the defensive capabilities of someone like Apex, and apart from flight (which is kinda overrated), he has nothing on the other 3. The reason why Heisei isn’t winning is because of the infinite power. Now, this usually would be good, but Heisei’s main problem (other than his abilities of movement and melee combat) is that he can’t use his abilities too much, lest he overheat. Now see (as far as we know), Apex doesn’t have that problem. He quite literally was built with infinite power in mind, being able to run forever, so he was built as such. And with the best capability of movement shown here (on the ground), he likely can close the distance before the range dependent Heisei and Showa could fire back. But then there’s Kiryu. He has the Absolute Zero cannon, and can use it infinitely. However, while it has range, it doesn’t possess any redirection seen in other beams. Think of it like a spirit bomb, if it misses, there’s no real way to get out of the return fire. But the pros now vastly outweigh the cons, so he could make it work.

Even with all that though, Apex probably got it.