Alternate universes are quite popular too. In these fanfictions, the settings of Naruto and Zatch Bell are completely changed. Maybe Naruto is set in the world of Zatch Bell, or the other way around. This allows for a lot of creativity as the writers can re - imagine the storylines, the power systems, and the cultures of the two series in a whole new light.
You can start by looking on fanfiction websites like FanFiction.net or Archive of Our Own. They usually have a large collection of fanfictions related to various series, including Naruto and Zatch Bell. Just search for the relevant tags or keywords.
One common theme is friendship. Since Zatch and Tia are friends in the original series, fanfictions often explore their friendship further, like how they support each other through tough times.
One frequent theme in 'zatch bell x penny fanfiction' is adventure. The two characters might embark on a journey together, facing various challenges along the way. Additionally, the theme of self - discovery can also be present. As they interact with each other, they learn more about themselves. For example, Penny might discover a new side of herself through her relationship with Zatch Bell.
One common theme is the confusion that comes with the body swap. Characters have to deal with being in a different body and all the challenges it brings, like not knowing how to use the new body's abilities.
One popular 'zatch bell zeno fanfiction' might be those that explore the deeper backstories of the characters. For example, a story could focus on Zeno's early life and how he came to be the way he is in the original series.
Social media groups related to 'Zatch Bell' can also be a good source. For instance, on Facebook or Reddit groups dedicated to the series, fans might post links to their 'zatch bell zeno fanfiction' or talk about their favorite ones.
In my opinion, it's hard to say. The anime can be more accessible and exciting, while the manga gives a purer form of the creator's vision. You might want to try both and decide for yourself.
In the end of the Zatch Bell manga, there's a big showdown and the story ties up loose ends. The characters grow and achieve their goals in a way that feels right for the story.