I'm not sure who the 'best' is as it's subjective, but some popular authors might be those who have a large following on fanfiction platforms. Look for ones with high ratings and lots of reviews. For example, there could be an author named 'RoseWriter' who is known for her detailed characterizations of Emily and Spencer.
In some fanfiction, there are storylines where Emily and Spencer are in a parallel universe. In this universe, they are the only ones who remember the events of the original Pretty Little Liars world. They have to figure out how to get back to their own world while also facing different versions of their friends and enemies. It's a really exciting concept that allows for a lot of creativity in exploring their characters.
If Emily dies in fanfiction, it could lead to some interesting plot developments. Maybe the other Liars would be more determined than ever to solve the mysteries they were facing, as a way to honor Emily's memory. However, it would also mean losing a key character in the story. Her athletic abilities and kind heart were important elements in the group, and without her, things would be a lot different.
One way fanfiction might deal with Emily's PTSD is by showing her in therapy. This could be an interesting angle as it allows readers to see her work through her issues. Her relationship with the therapist could be a key part of the story, with her either being resistant at first or really opening up. Also, her friends' reactions to her PTSD can be explored. Some might be very supportive, while others might not fully understand what she's going through.
Love and self - discovery are also big themes. Emily's journey to find true love and understand herself better is often at the center. Some fanfictions show her exploring her sexuality in new ways or finding love in unexpected places, which helps her grow as a person.
Another reason is that they both have had their own share of troubles in the show. By pairing them in fanfiction, it gives the writers a chance to show how they can heal each other. Spencer, with her family problems, and Caleb, with his past in foster care, can find solace and love in each other. This aspect of two damaged souls coming together is very appealing to many fans who write and read fanfiction about them.
One common theme is forbidden love. Since there are so many secrets and complications in the show, this often translates into their relationship in fanfiction. Another theme is mystery, as both characters have their own secrets, and fanfic writers like to explore how these secrets affect their relationship.
In fanfiction, Wren and Spencer often have a complex relationship. Sometimes, they are depicted as having a secret, passionate affair. Wren's mysterious nature adds an element of intrigue to their connection, while Spencer's intelligence makes their interactions intellectually stimulating.
One key element is the character interaction. How Spencer, with her intelligence and complex personality, interacts with Dean, who likely has his own set of skills and traits. Another is the setting integration. Incorporating the dark and mysterious world of Pretty Little Liars with Dean's possible role in it. Maybe he could be helping to uncover the 'A' mystery or dealing with the other secrets in Rosewood.
There are many great writers out there. Some popular ones are often those who are really good at capturing the personalities of Spencer and Toby as they were in the show. For example, some writers on fanfiction.net have a large following for their PLL fanfics. But it's really subjective, as different people like different writing styles.