Personally, I prefer the pre-finished flooring. When the environment can be controlled to apply stain and poly, there is a lot more that can be done. The job is THAT much better.
Usually, unfinished flooring gets 4 coats of poly, maybe 5 if the installer is a real pro. In a factory where pre-finished flooring is made, as many as 10 layers of poly can be applied because one can control the environment. THAT'S a big advantage.