I like ASW approach - Smaller ships are based on large amount of fast-firing blob turrets. Corvettes and destroyers have dedicated, also fast-firing cannon turrets. I made my Ancients for somekind of alternate reallity, where they survived because something helped them by destroying the Lucifer. Limited usage of beam cannons fits to Ancients in my opinion. Minos is supposed to be armed with plethora of heavy cannons similar to those from ASW, but spinal turret was supposed to be some remaining beam cannon. Perhaps BGreen equivalent.
Torpedoes are quite low-techish for me. My interpretation of Ancients is suposed to be sophisticated and exotic race, and both FS1 and FS2 shown why. All all projectile-based weapons are
Torpedoes fits to terran the most, in my opinion. If I am the one, who decided what each race should be armed, I would go with railguns and torpedoes for GTA, plasma cannons and swarm torpedoes for Vasudans, beams for Shivans and plasma cannons for Ancients.
Guided energy weapon is tempting. Basicly a standard torpedo from gameplay standpoint, but with invisible model and laser bitmap instead. Or... Perhaps no bitmap or trail, but particle generator? I succesfully made one of my favorite weapons from Exile with sole particle generator. Guided energy weapon would fit to Ancients due to exoticness of something like that, but I would use this for Nightmares instead.