It's hard to say who the 'best' is as it depends on personal taste. However, some popular authors in the fanfiction community might include those who have been writing for a long time and have a large following. For example, some authors on platforms like FanFiction.net or Archive of Our Own have a reputation for creating engaging Alice and Jasper stories.
One interesting story could be about Alice and Jasper's adventures before they joined the Cullen family. They might have had encounters with other vampires that shaped their views on co - existing with humans.
The theme of loyalty also pops up a lot. They are extremely loyal to each other and to the Cullen family. Fanfictions often explore how this loyalty is tested, like when faced with threats from other vampire clans, and how they always come out stronger together.
One great 'Twilight Alice Jasper Fanfiction' is 'The Bond Beyond Blood'. It beautifully explores their relationship in a world filled with the unique lore of Twilight. It shows how their connection is not just about being vampires but something much deeper on an emotional level.
Another theme is the struggle with their vampire nature. They are vampires in the Twilight world, and fanfictions sometimes explore how they deal with things like bloodlust and fitting into the vampire society while maintaining their relationship. It's interesting to see how different authors handle this aspect.
Love and loyalty are common themes. Their relationship is often explored in depth, showing how their love for each other endures through different challenges. For example, in many fanfictions, they face threats from other vampires or difficult situations within the Cullen family, but their loyalty to each other never wavers.
Their relationship would change in that they would have to be more open and communicative. Since Twilight is new to their world, they would need to share their experiences and knowledge freely. This would make their bond stronger. For example, Jasper might teach Twilight how to better use her senses in combat situations, and Alice would show her how to dress and present herself in the vampire society. This would create a deeper sense of family among them.
There are fanfictions that focus on Alice and Jasper's relationship in different scenarios. Maybe a story where they face a new threat together and how their bond helps them overcome it. In some fanfictions, they might have to deal with a vampire from their past who has a vendetta against them.
I'm not a huge fan of lemon fanfics in general, but if it's about Alice and Jasper from Twilight, it could be really interesting. Maybe it focuses on their relationship in a more steamy or different way than in the original books. It might explore some uncharted aspects of their love story.