
Note: I'm rather a speedrunner (if 6,5h game is speed run - I don't know!), so usually I don't have time (or guts!) to farm Phoboses, kill every Ferian Mine etc. (God! My english SUCKS!).
IM90 Multitarget Blaster. Used twice (+120% & +60%). Relatively fast, but easy (=boring) method.
Lamplighter Prototype. Used once, in 0.99c. Unstable, boring, dangerous, but without Iocrym Sentinel Threat it was rather easy kill.
Lamplighter Archcannon. Used maybe 5 times. Very easy kill. Boring and tasteless.
+150% Heavy Ion Blaster. Used today. Good and affordable weapon. And you don't need Hyperion to kill ICS

Ares Positron Cannon (fast). TRY IT IF YOU DARE. In 0.99c it took me literally 2,5 hours (yes - it's not a mistake - ~150 minutes!) to kill ICS with it. I don't know if it is possible in 1.0x version.
Things to try - IFC, Ferian Plasma Cannon, Xenophobe Ion Lancer. Any other ideas?