Finally completed the game. Love it but found the endgame to be a slog of neverending defense of havens and clearing out lairs and nests, the last battle is even worse. Found the Sniper/Inflitrator to be the go to combo that works for most of my battles. Suit them in Infiltrator gear, get all the stealth augments, I can run them anywhere without cover almost all the time. See an enemy, take a shot with the Raven sniper, most of the time it's one shot one kill with the stealth damage bonuses, even more so if you have the Sniperist 30% dmg perk. They're excellent against Chirons too, can get them most of the time without being spotted, once the Chirons' abdomens get damaged they're useless. If they do get in trouble, deploy decoy, vanish and run away. They're like squids, love them. I always have 2 of them in any squad.
Always brought a couple of heavies with Destiny III mounted. Never had a problem with Sirens with those and snipers around. If I spot a Siren, the Destiny III takes care of its head and it loses the MC ability. 999 range and 100% accuracy for 1 AP can't go wrong.
Also have a couple of assaults that are combo with the heavy or tech classes. I don't use them like some people which is to dash around and kill with a shotgun. I use them mostly to pass AP to the Sniper/Infiltrator so they can take another shot. Guess that's my playstyle. Lastly, I have one tech that goes around healing people or deploying turrets.