Let's take a look at the advantages and disadvantages of the different guns:
Laser Cannon:
Low power consumption
Low damage potential
High refire rate
High range
Analysis: one pair is enough to down light fighters in WC 1/2, but WC3 or later requires at least two pairs to do worthwhile damage.
Mass Driver:
Low power consumption (regular) / medium power consumption (Heavy/charging)
Medium damage potential (regular) / High damage potential (Heavy/charging)
High refire rate (WC 1/2) / medium refire rate (Priv, WC3/4/P)
Low range
Analysis: A good gun that packs a decent punch with a good refire rate, but the short range is bad for those who prefer to shoot at their enemies from a distance.
Particle Cannon:
Medium power consumption (regular) / low power consumption (pulse)
High damage potential (regular) / low damage potential (pulse)
High refire rate (pulse) / medium refire rate (regular)
High range
Analysis: The regular particle cannon is the most energy efficient gun in the game, being the only one to cause more than 2.0 units of damage per GJ of energy expended. It is my personal weapon of choice. The Pulse partical cannon is more of a machine gun, firing rapid, low-damage shots.
Tachyon Cannon:
High power consumption
High damage potential
Medium refire rate
High range
Analysis: The Tachyon cannon packs a heavy punch that is exceeded by only the Plasma cannon, and it does so with lower power consumption. In groups of four, these guns can make short work of any fighter, as evidenced by the overwhelming attack power of the Excalibur.
Reaper Cannon:
Low power consumption
Medium damage potential
Medium refire rate
Medium range
Analysis: The Reaper cannon is superior to its predecessor, the Ion cannon, having a lower power consumption with a slightly higher damage potential and refire rate. When given a choice between the two, the Reaper cannon wins hands down.
Ion Cannon:
Medium power consumption (regular) / Low power consumption (chain)
Medium damage potential (regular) / Low damage potential (chain)
Medium refire rate (regular) / High refire rate (chain)
Medium range
Analysis: The regular Ion cannon is the most energy inefficient of all guns used by the Confederation, consuming 30GJ of energy to do 30 points of damage. Its only saving grace is that it has a longer range than the Mass Driver; in all other respects the Mass Driver outperforms it. The Pulse Particle cannon is like a machinegun, firing fast, low-damage shots.
Stormfire Cannon:
Zero power consumption
Medium damage potential (Mk2) / Low damage potential (Mk1)
High refire rate (Mk2) / Very high refire rate (Mk1)
High range (Mk2) / Low range (Mk1)
Analysis: Both models of Stormfire cannon can rain death upon enemy ships...as long as the ammunition holds out. Be careful using the Mk1, as Black Lance pilots like to cut the throttle when you are tailing them closely.
Plasma Cannon (WC 3/4 version)
High power consumption
High damage potential
Low refire rate
Medium range
Analysis: The Plasma cannon has higher power consumption and a lower refire rate than the Tachyon cannon. Go with Tachyons if given a choice.
Plasma Mortar (WCP version)
Very high power consumption
Very high damage potential
Very low refire rate
Medium range
Analysis: The Plasma Mortar can take out light fighters in one shot--which is good because the two-second refire delay means that you may only get the one shot. In addition, it is the only gun that can destroy capship components in WCP. It is a great heavy hitter, but I would like to have another set of guns for backup for when I can't afford to wait through the refire delay.
Dust Cannon:
Low power consumption
Medium damage potential
Very high refire rate
High range
Analysis: The Dust Cannon's individual shots do moderate damage, but its real power comes when you can bring it to bear on a target for at least a full second--its machinegun-like barrage will tear anything apart.
Neutron Cannon:
Medium power consumption
Medium damage potential
Low refire rate
Low range
Analysis: The neutron cannon was a favorite up until the end of the Kilrathi war, when it was apparently realized that the Particle cannon could pack almost as much punch with a longer range.