To clarify the question, is it why is Visualize better than Vray Renders?
Presuming that it is, here is the response:
Visualize runs upon iRay render engine, Vray is a similar but different engines produced by Nvidia.
Iray is a path tracer, Vray is a ray tracer
The main difference is that Vray can split light/camera rays into sub-rays. So when a ray hits geometry, it splits into several secondary rays.
Iray cannot split the rays, it simply would trace a single secondary ray when it hits geometry. Iray is actually a play on words for Eye Ray, ie. just calculating the single ray as it goes.
So what does this mean for a user?
Vray will take longer to give you a visual feedback as there are more calculations needed to reach a pass. Iray on the other hand will be quicker to render the pass and give you a visual feedback alot quicker. It is then a progressive render, scaling quite nicely to remove the noise etc with each pass (especially with the new Denoiser).
So it is more a question of usability, where Iray will give you a visual feedback alot quicker than a Vray render.
Both are great renders and I wouldn't want to say which produces more realistic results!
Hope that the above makes sense!