King Dark vs Atom Smasher: who would win?

Too close to call

King Dark · Kamen Rider · Base

Tier
LOW 4-C
Attack Potency
Small Star Level
Speed
Superhuman, up to Speed Of Light
Durability
Small Star Level

Atom Smasher · DC · Base

Tier
LOW 4-C
Attack Potency
Small Star Level
Speed
Superhuman, up to Relativistic+
Durability
Small Star Level

A heuristic estimate from normalized VS Battles Wiki stats: tier, attack potency, speed and durability.