Which shipmates are the best fighters? Who do you take into battle?

well If i dont want to think about it I take Vetra and Drack they can survive on their own but once you level them up all squad mates generally do a good job except Cora. Cora thinks charging a fiend is a good idea. Cora also likes being eaten and dying >.>

Well... after completing her loyalty mission, Cora can shoot cryo ammo (level 6 evolution from the ability tree), which make a great primer for a Ryder vanguard.
Even on Insanity, Fiends and their blue variation tends to… melt quite fast, when you have a perma priming on them. So, as a biotic Vanguard, I like Cora and Jaal the most as companions (dat shadow strike), switching Cora for Peebe only VS Architects (for the invasion debuff)

Entirely depends on build and play style I'm going with but with my combat-tech build using concussion shot, overload, and incinerate...Drack and Cora were my mainstain. Drack is just difficult to kill and melees the hell out of everything, keeping tougher enemies occupied. Cora's shield boost is a damn lifesaver on insanity and she's great at detonating combos. I can count on one hand the number of times I had to revive them while other team members were more "needy." Since both these characters are aggressive spec'ing appropriately is important.

Drack and Drack. Also Drack. I've got 3 planets at 100% and he's died once on me playing on hardcore.  Plus, I'm playing an adept and I like someone who keeps the enemy from rushing me, who I don't have to go pick up (Cora).

I usually bring along Jaal since I'm on Angaran planets and it seems appropriate for RP reasons, and he's alright, but Vetra would probably be my second choice in terms of battle.

Drack and Cora

Drack and whomever I feel like at the time.

Drack and Vetra.

A few people mentioned Cora's Cryo Ammo, but Vetra has Disruptor Ammo. She has this on a Turbocharged Cyclone. She also has a very effective defensive power, in lieu of Cora's charge-and-die approach. I do like Cora, since she pairs very well with my biotic; and I've honestly had little issue with her dying. Vetra, though, is the best pure soldier in the game. Paired with Drack, you have non-stop Fire and Tech explosions; krogan roars; and Vetra's turbocharged Cyclone whirring. It's beautiful.

I vary my squad based upon mission and story needs, though. Everyone brings something to the table. I'm not a big Liam guy, since he melees and does so less well than Drack; but he has a nice power loadout. I may try to use him slightly more next time. His behaving like he's 7yo, among other things, grates my nerves, a bit.

Vetra and Drack at the moment. I was using Vetra and Cora but when I got Drack, Cora got replaced with him.

- Wolf

Drack because he's a living bait, help take some heat off of Ryder, Cora sometimes because she can generate shield & help out Drack.

I wish Jaal is half as good of a sniper as Garrus(ME3)/Legion(ME2).
& Liam half as good as Vega(ME3)
& Peebee as good as Tali/Liara.

I think the squadmates in MEA are rather weak compared to the OT.

I usually use the companion that seems to fit in best with the story.

If I am mainly interaction with a particular species I will choose matching species. So Jaal for Angara, Vestra for Turian etc.

For playing with Remnants PeeBee, kill Kett Drack, Nexus personnel Vestra, Human settlers Cora/Liam etc.

Whatever I feel seems to fit at the time.

Drack can tank nicely unlike the other squad mates. I've seen him fight face to face with some strong enemies and survive for ages.

Drack and Vetra is my default. But after reading this thread, I'm thinking of trying Drack and Cora