While the heavy metal slugs and flechettes thrown by projectile weaponry tend to be more damaging, the lack of recoil for non-Heavy energy weapons makes them more accurate, granting them a +1 bonus to hit rolls.
Energy weapons are very popular on more advanced worlds, as a soldier can carry far more ammunition in the form of energy cells than they can carry bullets. Range and accuracy are often superior, though the infrastructure necessary for maintenance and repair of these weapons is substantially higher.
Pistol-sized energy weapons count as one item of encumbrance.
Thermal pistols replace the beam of a laser with a small sphere of magnetically-shaped plasma. The spheres tend to dissipate at much shorter ranges than a laser beam, but do significantly more damage to targets within range and are not affected by ambient particulates.
They tend to be extremely loud in operation.