TYVM ALL, PPL:)
For Marsecs, the R-Rifle sounds like a deal to me. I have these in all of my bases and assault ships (with a lot of ammo - mandatory for all weapons in my case) Yao can carry this one and a SuperMagnum or an EuroSyn Laspistol plus grenades and a Shokafist... Yea, this looks nice enough. I suppose that an Autolaser could also be used? Hit from behind? Dunno. I always face them frontally. Dunno why, maybe my tactics is just like that. I could change it no prob - I like changes. Could a Recoilles Rifle also punch through a Merc?, BTW?
My default mid-game loadout is anti-armor. It includes 3-5 frontline Junkmasters with ES laspistols and either axes or pikes, backed up by 3-5 in Tactical, Hover, or Sniper with ES laspistols and RRs with 3 shots each. I also currently have a Freak Gal in Hover with 97 strength and an anchor (easily over 200 damage) which she can carry with an ES pistol.
The axe inflicts more raw damage, but the pike has 60% armor reduction, a 3 tile range, and snap shots allowing it to destroy terrain. The RR obv kills armor reliably. Nothing survives the anchor. ES Laspistols can whittle Bodyguards down but should be applied to the rear armor if possible. Two of the hovers (or snipers) usually also have fireball launchers, which leaves them a bit overweight until they get to sniper positions and drop either their RR or fireball launcher. Everyone carries a Smoke, a Hallucinogen, and a WP grenade. 1-2 Tactical or Snipers can carry Surgery Kits (hovers lose the extra RR shells). Junkmasters carry water and the anchor-gal carries beer for energy.
I keep plenty of other equipment on board: Hand cannons, rocket launchers, M-Lasers, and so on, but at this stage in the game, the above loadout works everywhere (on Earth, above water). Its main weaknesses are that the ammo is expensive and you aren't stunning much. Remember, though, that the RR can be used to bash some skulls in a pinch, and the Junkmaster gauntlet does great damage.
I found other heavy weapons like the LC and LACC to be more cumbersome than I prefer. Everything listed above was an evolution of pragmatism, trying lots of things and applying Occam's Razor. It works in Jack Sparrow.