Thor wins, he has far to many ways to put superman down in a fight. Thor can and has countered speedsters as fast as or faster than superman. Thor has Godlike reflexes and superman cannot attack at light speed anyway.
The only speedsters that could move beyond light speed in an attack ( well at least 2 that are worth mentioning ) are flash and gladiator. Those 2 could defeat thor with speed. Flash fought zoom in a fight that was measured in seconds and superman was a statue. Reed used tech to boost theirs and thors speed to where time froze ( they were moving far faster than flash and zoom were moving) Gladiator increased his speed to not only fight thor at that speed, but he walked and talked with them at that speed. What would happen if the tech reed used to boost their speed suddenly failed? Long story short, thor and superman are around the same speed combat wise, so speed here is not an issue. Thor wins by having that blasted hammer and far greater powers.