Tier by tier weapon comparison, using the values provided by Maiden's GC2Types.xml, using Mass Drivers as nominal cost/power and nominal power/size. Battles were simulated using $100k bc worth of ships in fleets, throwing fresh fleets against fresh fleets, then injured, until one side was dead. The simulation is run several times for each weapon combination, hull size, and tier.
Note that I consider the simulation "close" if the winner has <10% of their original ships remaining, a solid win from 10-25%, a decisive win from 25-40%, and anything over that is crushing.
Tier 1:
Beams are 50% more expensive and have 25% more power/size.
Missiles are 32% more expensive and have 53% more power/size.
Small hull, no mini: Beams beat missiles. Drivers win decisively against both.
Medium hull, no mini: Missiles and drivers about equal. Each win solidly against beams.
Tier 2:
Beams are 50% more expensive and have 25% more power/size.
Missiles are 37% more expensive and have 36% more power/size.
Small & Medium hulls, no mini: Missiles beat beams. Drivers win decisively against both.
Large hulls: Missiles beat beams. Drivers beat beams decisively and missiles solidly.
Tier 3:
Beams are 24% more expensive and have 28% more power/size.
Missiles are 21% more expsneive and have 9% more power/size (small hulls) up to 22% more power/size (big hulls)
Drivers have solid wins on all hull sizes. Beams and missiles close on small and medium hulls, Missiles beat beams solidly on large and huge.
Tier 4:
Beams are 39% more expensive and have 42% more power/size
Missiles are 27% more expensive and have 11% more power/size (small hullls) up to 23% more power/size (big hulls)
Drivers have solid wins on all hull sizes. Beams and missiles close on small hulls, Missiles beat beams solidly on medium or bigger.
Tier 5:
Beams are 33% more expensive and have 28% more power/size
Missiles are 22% more expensive and have 0% more power/size (small hulls) up to 13% more power/size (big hulls)
Drivers have decisive and occasionally crushing wins on all hull sizes. Missiles beat beams on all hull sizes.
God tier:
Beams are 21% more expensive and have 38% more power/size
Missiles are 3% more expensive and have 25% more power/size (small hulls) up to 42% more power/size (big hulls)
Drivers win decisively on all hull sizes. Missiles beat beams on all hull sizes, but its close.
Conclusions:
* Mass Drivers are too good (or cheap, take your pick). They allow you to get a lot of metal in the air, and even though pound for pound they don't do as much damage as beams or missiles, there's enough HP left to carry the day, quite decisively most of the time.
* Beams and missiles are close. Missiles have the edge, but they're more expensive to research and have the lowest utility due to their size.
* due to how sizeMod works (constant + to weapon size regardless of initial size), beams get heavily penalized on larger ships. This really hurts them.
* I haven't taken defenses into account. That's an order of magnitude harder to code.
* I owe OShee an apology for accusing him of underestimating the value of per-fleet attack. I overestimated it at least as badly.