Democratic det, no contest. The grenade is good, the armor is good, the Eruptor might be one of the best primaries in the game.
It's basically a light autocannon that can close bug holes, inhumanly kill and maim most enemies, and it does heavy damage. As a primary. That means it can kill automoton heatsinks on things like mortars too. It can also blow over shields on harvesters. It can kill heavies and flying aircraft.
The only downside are the ergonomics aren't great at first (the reticle is slow to move). This can be upgraded by using it and then buying the weapon upgrades that prioritize the "ergonomic" modifier. It becomes pretty dang fast at level 23 ish.
Do not use it at close range, or around allies. Back at release, it was even more lethal, lol. And in fast enemies, it can be a danger to you. Keep a good, fast secondary to get enemies off you.
The desert dlc is also really good, the Solo Silo is absolutely, certifiably cracked. It's a laser-guided (if you hold it down) 500kg, or a dumbfire (if you click) missile. It's way more lethal than a 500, because it pretty much never misses its target.
If you order one, the cooldown will start again. So you can have two back-to within seconds if you want as soon as two minutes into a mission. It takes your third gun slot, but you can equip a backpack stratagem or you want more protection, or an EAT or flame EAT if you need constant AT potential while the solo silo is on cooldown.
As a bonus, it looks cool as shit if you are looking towards the launch site from a couple hundred meters out when you call it down on a target between you and it's launch site. Pocket ICBM.