Guardian has the best frontal firepower of all ships, just because it can spam Hammer Barrages all day, every day, and not run out. 6000 damage every 5,15s is about 1165 DPS. You can put storm needlers in the hybrids for constant 3000 damage to shields and now the only issue is that Hammer Barrage is inaccurate over long distances. It's still better than alternatives, which have much longer firing cycles (5,15s for Hammer Barrage, 20s for Squall, 17s for Cyclone, 15s for Hurricane, 9s for Locust).
Longer ranged loadouts (something like double Mark IX, double Haephestus) superficially don't have as much firepower, but firing at a target that can't fire back has the best damage-to-flux ratio of all possibilities.
I don't recommend making Guardian capturable, because with player piloting, it's capable of defeating everything else in the game on its lonesome.