What is the best way to connect 3D printed parts? I want to print a model of an animal cell.

What I have so far: I managed to use different colors to print out the different parts of the cell.
My question is: what is the best way to connect plastic 3d printed parts?
Glue? Melted plastic? I need it to have a strong connection and not very visible when used well, and preferable dries fast.
For ABS print, I recommend acetone. It is not a glue, but it will dissolve the plastic a bit and if you apply it to both connecting parts and push them together, they will stay connected after the acetone dries. However, it does not dry very fast and you have to be careful not to destroy the object.

For PLA I usually use regular super glue (Cyanoacrylate).