Misty, Taissa, Shauna, Van, and Lottie
In the adult timeline, every relationship is complicated. Having survived the Wilderness and the aftermath of Jeff's blackmail and Natalie's death, the remaining survivors are still being impacted by all they have gone through. While season three does spend some time spreading out its adult main cast, what they do provide when the group is together is some of the most integral storylines to moving the adult storyline forward. Their individual arcs are interesting, but they are at their best when grouped together, constantly showing the remaining connection that exists between them. They understand each other like no one else does.
Shauna may not easily fill the Natalie-sized hole that Misty wants her to, but while Shauna may not consider Misty a friend, she still understands Misty's devotion and connection to the remaining Yellowjackets better than Walter could. Walter views the Yellowjackets as not being Misty's friends and believes that Misty deserves better, such as someone like him who is always ready to step up for Misty if and when she needs it. The idea that Misty's friendships with the remaining survivors may not be exactly how she thought it was may be true, but that does not mean they do not still hold a connection, which is partly why Shauna knows that Walter viewing solving Lottie's murder as playing a game with Misty rather than viewing it as a friend's death that needs to be solved is the wrong perspective. They are also not afraid to question if another committed murder, such as Misty's easy way of accusing both Taissa and Shauna of killing Lottie without blinking an eye.
Their energy together all together is chaotic, which is one of the most enjoyable parts of the adult timeline. Shauna, Misty, Van, Lottie, and Taissa never have to hide who they are when they are together, and it allows for some of the show's funnier moments. Van's death results in challenging Taissa and Shauna's friendship, and Melissa's return fuels new possibilities in terms of character dynamics, especially as the door is open for her to come back in other capacities moving forward. Lottie's death is the catalyst that brings the group together again, but it is Van's death that may see the splinters in their relationships start to show.
The adult timeline does not have the same benefit as the Wilderness timeline to constantly have the main characters grouped together, due to their individual lives. However, their individual lives are no match for the scenes when they are all interacting and dealing with the havoc that they themselves have created. At the conclusion of season three, Yellowjackets sets up significant conflicts for what would come next, including an alliance between Taissa and Misty that would be bound to be satisfying, given these two have yet to truly be tied together in either timeline.