It depends on personal preferences. Some people might think Tokyo Ghoul is better for its original story and character development. Others might prefer Tokyo Ghoul:Re for its continuation and new plot twists.
Well, for a Tokyo Ghoul fan, reading fanfiction while being a fan of the original can be a mixed bag. On one hand, it's exciting to see how other fans' creativity expands the world. For example, there could be fanfictions that focus on the backstories of minor characters. However, sometimes the quality can vary. Some might not capture the essence of the Tokyo Ghoul world as well as others. But overall, it gives a chance to delve deeper into the fandom.