I play with a group of 3 or 4 and all my partners like to specialize in CC with Zero, sniping with Maya and the other uses Maya with elemental smgs so I have been covering the assault rifle, SMG, and rocket launcher area. It makes me feel more like a recon commando.
I use a detonating assault rifle as my main weapon. then a static shotgun, caustic revolver and incendiary smg for specific defences. He seems to be most effective with assault rifles and rocket launchers though
? If you are heavy into the Guerrilla tree, which is really good for the first playthrough, just use your best weapon or even better tune to three elemental weaknesses of what you're fighting. Don't put too much thought into what genre of weapon you should be using.
Yes, you can spec him to have more ammo for an assault rifle, and one of his mods is directly for assault rifle damage, but honestly, it's like a single peanut on top of a sundae, not even a cherry.
You're going to be switching weapons, there's no need at all to focus on anything other than good guns.