Excalibur is a great choice. It's a well - balanced Warframe that can handle a variety of situations in the story. Its basic abilities are useful for combat and crowd control. For example, the Slash Dash can quickly close the distance to enemies or escape from dangerous situations. And its Radial Javelin can deal significant damage to multiple foes at once.
I would say Mag. Mag has abilities that are very useful for story missions. Her Pull ability can draw enemies towards her or pull items from a distance. This can be used to disarm enemies or gather resources easily. Her Crush ability can deal a good amount of damage to grouped - up enemies, which often happens in story battles.
The Second Dream is one of the best. It really delved into the mystery of the Tenno's origin. It was a mind - blowing experience as it revealed things about our character that we had not known before, like the true nature of our connection with our Warframes.
The Heart of Deimos is a great one too. It focused on the Infested and the secrets of Deimos. It had a very unique atmosphere compared to other parts of the game. The story had a lot of exploration and discovery elements which made it interesting. The way it tied in the lore of the Infested was really well - done.
Gale is another excellent choice. His pursuit of magic and the mystery surrounding his condition with the Netherese orb. His relationship with Mystra and his attempts to regain his former status contribute to the story in many ways. He also has a lot of knowledge about the lore, which enriches the story as you progress.
In the BG3 story, some of the best companions are Shadowheart. She has a mysterious past and her own beliefs that add depth to the story. Another great one is Gale. His knowledge of magic and his personal quest for power and redemption make him an interesting character to have around.
Dogmeat is a must - mention. His loyalty is unrivaled. He doesn't have complex motives like some humanoid companions, but his simple presence and the way he helps the player in combat and exploration tell a story of pure loyalty. And Curie. She starts as a simple caretaker - like robot but evolves into a complex synth with her own dreams and desires, which is really cool.
Kwon is a great companion for the story. He has a strong sense of loyalty and his backstory adds depth to the overall narrative. His combat skills also come in handy during various missions.
Wyll is an interesting companion. He made a pact with a devil, Mizora, in order to gain power to be a hero. His story is all about his attempts to redeem himself and break free from the devil's hold. His relationship with the other companions and his decisions based on his moral code are key parts of his story. Karlach is another great companion. She has a heart of gold despite being a tiefling. She escaped from the hells but is haunted by her past there and her time with Zariel. Her story is one of survival and finding a place in the world.
Lae'zel has a fascinating story too. Being a Githyanki warrior, her loyalty to her people, her beliefs about the creche and her experiences that make her question and grow throughout the game add depth to her story.