It would depend on your caracter. For example If I give 100m for tempo to my hockey player, they want to go all out all the time.
For some 300m with good technique is a hard thing to do (for non-sprinter athletes).
200m is often a good middle ground.
For 400m, I would prescribe only if I know you have perfect technique, but even It’s too long.
200-200-200 (2min rest between reps / 5min rest between sets)
200-200
progress to
4-5 x 200m (2min rest between reps)