Which will be better, a single FixedUpdate with complex code or many FixedUpdate with simple code?

Title said it.

Lets say i will need to have like 100 moving GameObject in my scene, i need to move them in my code. I can have a manager that manage a full list of these 100 items, and only perform their movement in 1 single FixedUpdate with complex code, or perform it separately into 100 FixedUpdate with much simpler code(attach to each GameObject) ?

 

There isn't exactly a right or wrong answer here, but the latter is usually how you want to go. Usually; there are plenty of times where it makes more sense to control a bunch of objects in one manager script. Either approach works fine, so just do whatever makes the most sense, bearing in mind that simpler-to-understand code is almost always better in the long run (so that others can understand what you wrote, and so that you can understand what you wrote 5 months ago.)