I'm not sure about who the 'best' are specifically, but you can often find good ones by looking at the top - rated stories on fanfiction websites. Some authors might be really good at exploring the darker aspects of a vampire Stephen Strange, like his moral conflicts.
One interesting Vampire Stephen Strange fanfiction could be about him using his vampire powers to fight off dark magic threats in a different dimension. He might have enhanced speed and strength which he combines with his sorcerer skills.
I really like 'Strange Encounters'. It delves into an alternate universe where Stephen Strange has to face a different set of challenges. The author does an amazing job of creating a new and exciting world for Strange to navigate, and the way they write his character is very true to the original while also adding new dimensions.
The arc reactor in fanfiction involving Stephen Strange can also be a source of conflict. Some might write that the energy from the arc reactor is disrupting the magical balance that Strange is trying to maintain. This could lead to a tense relationship between the two characters at first, but as the story progresses, they could find a way to work together to either control or utilize the arc reactor's power in harmony with magic.
There's also a fanfic called 'Love in the Mystic Arts'. This one combines the magical world of Doctor Strange with the relationship between Stephen and Christine. It has some really interesting plot twists where Christine gets involved in the magical realm more than she expected, which adds a whole new layer to their relationship.
Another theme is redemption. Sometimes one of them may have made a mistake in the past and the other helps them find a way to make up for it. For example, Tony's past actions causing destruction and Strange using his magic to help Tony see a new way forward.
You can find Stephen Strange fanfiction on websites like Archive of Our Own (AO3). It has a large collection of fan - created stories about various characters, including Stephen Strange. There are different categories and tags to help you find exactly what you're looking for.
Perhaps in the fanfiction, Harry Potter gets lost in the multiverse and ends up in the world where Stephen Strange operates. Strange takes Harry under his wing, teaching him about the different forms of magic beyond what he knows from Hogwarts. Harry, in turn, could introduce Strange to some of the more unique magical creatures from his world, like the Hippogriff.
I really like 'Strange Love'. In this fanfiction, the author does an amazing job of showing how the reader's presence affects Stephen Strange. It's full of emotional moments and some really interesting plot twists that keep you hooked from start to finish.
The theme of identity is quite common in 'female Stephen Strange fanfiction'. The female characters often have to define themselves in a world dominated by male characters like Strange. They might question their place in the world of the mystic arts and how they can contribute. Another theme is the idea of alternative perspectives. Since they are female characters, they may view the magic, the battles, and the relationships in a different way than Strange, which can lead to interesting plot developments and character interactions.