How to get the Ultimate squad makeup to face the greatest challenges
For the gamer who plays on the highest difficulty, the difference between arduous and repetitive deaths and success may depend simply on the composition of your squad. The one thing you have to remember is that there isn't just one 'Best Squad Makeup' - There are many variables at play. But the two biggest golden rules that should influence your decisions are : - Your character Class/Archetype - The type of Enemy you face As a team, you and your squad must work together as one. Shepard is part of the squad composition as much as any of your companions, and the Class you pick reflects your personal limitations. Due to this you should pick your other squad mates to complement that. For example: If you are a Biotic (Vanguard or Adept), you can easily control 'regular' enemy units that do not have shields, armor or barriers, however you will do poorly against shielded enemies, such as the Geth. Within those circumstances, EDI is the best choice. EDI is able to Overload those pesky shields, and Incinerate those tough armored units such as Geth Pyros/Primes. To further complete this, Tali makes the perfect addition. She is able to distract dangerous enemies with Combat Drones, such as Hunters, and can also help tear away shields with Energy Drain. Finally, her Sabotage ability is quite handy to set enemies on each other, taking off a great deal of pressure from you and your allies. If you are a Tech based class, then you should replace one of your squad mates with a character able to provide proper suppressive fire and a capability to deal with shields, such as Kaidan or Ashley. Additionally, their survivability is great against cloaked Hunters and Rocket Troops.
If you are taking on Cerberus, then you will need a companion who can soak a lot of damage and properly deal with close quarters combat. Cerberus is an enemy force quite adept at closing in and squeezing adversaries against a wall by constantly pushing them back. James Vega is quite suitable to take on the enormous amount of damage that can result from such close encounters. His Fortification ability combined with a Shotgun make him the perfect friend to deal with enemies in this situation. Guardians can also be counteracted efficiently with James, since he is able to soak the damage and also stagger them with Carnage. This leaves the other half of the Cerberus units to be dealt with; The Engineers, Nemesis and Phantoms, which favor shields. Once again, Kaidan/Ashley are the perfect counter to dealing with these units. They both can take a decent punishment and are well equipped to deal with those pesky shields with Overload/Disruptor Ammo. If you have Kaidan, his Cryo Blast works great for slowing down the Assault Troopers' advances, and can also help hinder/tear armor away from ATLAS mechs. Alternatively, Ashley is devastating with her combined Assault Rifle prowess and Marksman ability. If you do have Javik, he is an excellent secondary choice against Cerberus, as he can easily tear shields away from Guardians, send Assault Troops flying, and use Dark Channel against Phantoms or Cerberus mechanical contraptions. Finally, a Biotic is a great choice against Cerberus if you are a Soldier class yourself. When fighting the Reapers, you will be facing swarms of unprotected enemies at any given time, with their support units heavily armored. Due to this, Biotic allies are the prime choice, as they can effectively control the fodder with knock backs. Liara and her Singularities are perhaps the strongest tool you can use against large waves of Husks or Cannibals. By placing the Singularity at key choke points, you will levy much difficulty out of a fire fight and you will be able to use your own ammo much more efficiently. Additionally, her Warp ability is perfect for handling any Brutes, Ravagers and Banshees that come your way.
The optimal secondary choice against Reaper foes is Garrus. Garrus can effectively push back Husks with Concussive Shot, tear down armored Brutes and Ravagers with his Armor-Piercing ammo, and Overload the barriers of the Marauders and Banshees. Equipped with his trusty Sniper Rifle, Garrus will be able to pick off Cannibals from a good distance before the squad is overwhelmed. If any enemy manages to get nearby, precariously placed Proximity Mines can turn what looks like easy prey for the Reapers into efficient ambushes and traps.
Remember that the tactics mentioned for your Squad mates are also applicable to you, if you have those abilities. Crowd control and efficient management of your squad is key to hard mode victory.