The Andromeda Ascendant really should be allowed into this little free-for-all. The question, of course, is which form she should appear in:
heavy cruiser,
android avatar,
AI in a virtual reality environment,
pair of enormously huge planetary combat robots, or
horde of service androids with force lances?
Even if we limit the choice just to the android avatar, IG-88 should have a tough fight on its hands. Rommie apparently invested in armored internal systems after getting speared through the guts (rather like Data, actually). Rommie is also strong, agile, fast, has encyclopedic military experience and knowledge, knows how to apply it in combat, has a fully developed personality complete with humor, and has one unbeatable advantage: understated android cleavage.
If none of that works, just start with the barrage of kinetic kill missiles.