Your desired combat range depends entirely on your ship and weapon configuration:
All energy weapons are best used at close range with the exception of rail guns. (Though rail guns use ammo, they are often considered energy weapons due to their high energy consumption.) Under 150m is optimal for most.
Rockets and missiles are best used when at mid-range, around 150-200m. Be aware that all rockets have a safety range where they will not detonate. If your target gets too close to you, you will not be able to hit.