Check the table below for a complete list of eleven potential candidates for the suicide mission. The table tells about their unique powers, offer hints on where to find them and provides a valuable information about their specializations.
Don't forget that the list of powers available for each character includes their unique abilities which become available AFTER completing their personal missions.
You should know that the specializations of your teammates aren't an identical copy to what you can choose from while creating a new character. A perfect example to what I'm saying is Samara - she can use assault rifles even though she might seem as an adept. Make sure to rethink your choices each time before setting off on a new mission!
He can join your team after completing Dossier: Archangel mission [Omega - Archangel's base].
Normandy: Main battery on the third deck.
Specialization: combat / tech
Unique powers of this character: overload, armor-piercing ammo, concussive shot.
He can join your team after completing Dossier: The Warlord mission [Korlus - Blue Suns facility] and only if you decide to open the pod.
Normandy: Storage area on the fourth deck.
Unique powers of this character: incendiary ammo, fortification, concussive shot.
She can join your team after completing Dossier: The Convict mission [Prison ship Purgatory].
Normandy: Lower corridors on the fourth deck.
Unique powers of this character: warp ammo, pull, shockwave.
He joins your team during the prologue - Lazarus research station mission [Lazarus research station].
Normandy: Armory on the second deck.
Specialization: combat / biotic
Unique powers of this character: barrier, pull, incendiary ammo.
It can join your team after completing The Reaper IFF mission [Derelict Reaper] and only if you decided to activate the captured geth.
Normandy: AI core on the third deck.
Unique powers of this character: AI hacking, geth shield boost, combat drone.
She joins your team during the prologue - Freedom's Progress mission [Freedom's Progress].
Normandy: Office on the third deck.
Specialization: biotic / tech
Unique powers of this character: warp, slam, overload.
He can join your team after completing Dossier: The Professor mission [Omega - Slums].
Normandy: Laboratory on the second deck.
Specialization: combat / tech
Unique powers of this character: cryo blast, neural shock, incinerate.
She can join your team after completing Dossier: The Justicar mission [Illium - Spaceport].
Normandy: Observation room A (the northern one) on the third deck.
Important! Samara may be replaced by her daughter MORINTH if you choose a renegade ending of her personal quest. Morinth has the same powers and she even poses as Samaras in front of others.
Unique powers of this character: pull, throw, reave.
TALI'ZORAH NAR RAYYA
She can join your team after completing Dossier: Tali mission [Haestrom - Quarian landing site].
Normandy: Engine room on the fourth deck.
Unique powers of this character: AI hacking, combat drone, energy drain.
He can join your team after completing Dossier: The Assassin mission [Illium - Spaceport].
Normandy: Life support on the third deck.
Unique powers of this character: warp, shredder ammo, throw.
He can join your team after completing Dossier: The Veteran mission [Omega - Market district].
Normandy: Storage area on the fourth deck.
You can recruit this character only if you've installed Zaeed DLC!
Unique powers of this character: concussive shot, disruptor ammo, Inferno grenade.
Who should I choose?
The main factor you must take under consideration when choosing a team is your main character's class. It's always a good thing to have a balanced squad which would have one combat specialist, one biotic specialist and one tech specialist. Doing so allows you to be prepared for different kinds of threats. Naturally it won't always be possible to choose certain specializations and things may get even more complicated if you decide to choose a class which is a combination of two different specializations.
If you think of yourself as a more experienced player you may consider changing your team depending on the dangers of each mission. For example, you don't necessarily have to take a tech specialists if you'll be fighting organic targets or monsters, but you can take even two of them if you know that you'll fighting a lot of machines.
You pick a team each time when you leave Normandy and it's a possible to choose a different squad for each assignment.
Here are some of my suggestions for balanced, safe squads:
When Shepard is a soldier (combat specialist) - You should add Jack to your team in the early stages of the game, although you might want to consider taking Samara in her place after the asari has joined your team. As for your tech specialist, Miranda will do the job for most of the game, because she has learned a very useful Overload ability. You can exchange her for Tali or Legion later in the campaign.
When Shepard is an infiltrator (combat/tech specialist) - It's important to have a good combat specialist in your team - Grunt and Zaeed are the best followers you can hire for the suicide mission, however Garrus or Jacob can fill in the first spots until they've been unlocked. I would also recommend choosing a good biotic. Miranda will do just fine in the early stages of the game, but eventually she should be replaced by Jack, Samara or Morinth.
When Shepard is a vanguard (combat/biotic specialist) - Vanguard specializes in combat and biotics so you should definitely have someone in your team whose powers combine combat with technology. Garrus and Mordin are among the candidates and the good news is that can recruit them in the early stages of the game. If you don't want to have them both in your team then you may consider having one good biotic specialist (Samara) or one good tech specialist (Tali).
When Shepard is a sentinel (biotic/tech specialist) - A sentinel doesn't have anything to do with combat so it's extremely important to add at least one combat specialist to your squad (Grunt or Zaeed). As for the other crew member, depending on your preferred style of play you can choose a combat/biotic specialist (Jacob is a good candidate) or a combat/tech specialist (Garrus is a good candidate).
When Shepard is an adept (biotic specialist) - Make sure to choose a combat specialist so that you won't have to worry about enemies being focused on attacking your main character. Two best candidates for the job are Grunt and Zaeed, however you may consider choosing a partial combat specialist if you haven't unlocked them yet (Garrus will get the job done). As for the second team member, you should choose a tech specialist. It may be only a partial specialist at first (Mordin or Garrus) but eventually you'll have to make a switch to a full tech specialist (Tali or Legion).
When Shepard is an engineer (tech specialist) - I think it's fairly obvious that you'll have to choose two other specialists - a combat specialist and a biotic specialist. Jack is a great biotic, however you may want to consider hiring Samara (or Morinth) instead of her later in the game, especially since the asari can use assault rifles. As for a combat specialist, Grunt and Zaeed are the best choices, however can rely on Jacob's or Garrus's abilities if they haven't been unlocked yet.