One of the best for the story is Lae'zel. Her rigid Githyanki upbringing and her views on the world are constantly challenged throughout the story, which is really interesting. Gale is another important one. His knowledge of magic and his own self - imposed mission related to it are key parts of the story. And don't forget about Wyll. His pact with a devil and his attempts to do good in spite of it are crucial to the story's development.
For story, I'd recommend Shadowheart. Her loyalty to Shar and the slow reveal of her true self as the story progresses is fascinating. Then there's Astarion. His journey from being a subservient vampire spawn to potentially finding freedom is a great story arc. Karlach is also a good pick. Her bubbly personality combined with her tragic backstory of being in Avernus makes for a very engaging story element in the party.
A classic and effective party composition could be a tank, a healer, a ranged damage dealer, and a melee damage dealer. For example, a Fighter as the tank to soak up damage, a Cleric for healing, a Ranger for ranged attacks, and a Rogue for melee damage and sneaking around. This allows for a balanced approach in combat and different skills to be utilized during the story quests.
A party with a Cleric, a Rogue, and a Wizard can be great for the story in BG3. The Cleric can heal and provide support, the Rogue for sneaking and lockpicking, and the Wizard for powerful magic to deal with various challenges in the story.
Astarion is a great choice. His complex backstory adds depth to the story. He's a vampire spawn with his own motives and development throughout the game. Another good one is Shadowheart. Her mysterious past and her role within the Sharran cult bring interesting story elements. And Gale, his connection to the weave and his pursuit of magic in a rather dangerous way enriches the overall story experience.
A composition with a Ranger, a Cleric, a Monk, and a Warlock. The Ranger can be a ranged attacker and tracker, good for exploring and dealing damage from afar. The Cleric is essential for healing and also has some buffs and debuffs. The Monk is a unique melee combatant with high mobility and unarmed attacks. The Warlock has some interesting spellcasting abilities and can make pacts for different powers, which adds a lot of variety to the party's capabilities in the story.
One of the top characters for the best party could be Rena. She has strong healing abilities which are essential for the party's survival during tough battles. Another great addition would be Claude. His combat skills are quite good and he can deal decent damage to enemies. Also, Ashton can be a great choice as he has unique abilities that can turn the tide in battles.
Astarion is a popular choice for the romance story. He has a complex personality, being a vampire spawn with a troubled past. His journey of self - discovery and his relationship with the player character can be very engaging. His flirty and sometimes sarcastic dialogue adds charm to the romance.
The best party for BG3's story could be a Barbarian, a Druid, and a Monk. The Barbarian is great for raw combat power and can soak up damage. The Druid can transform and has a variety of spells for different scenarios. The Monk is fast and has unique combat abilities that can help in battles throughout the story.
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.
For the story, I'd say Sebille and Lohse are must - haves. Sebille's journey of revenge is full of twists and turns that are deeply intertwined with the game's story. Lohse's fight against the demon within her is both dramatic and engaging. Adding Ifan to the party also works well. His past as a soldier and his moral dilemmas add another layer to the story.