I'll give you my personal opinion on each for what its worth, but since you are a student you should try each so you learn first hand. Each renderer has its strengths and weaknesses and there is always a trade-off between speed and quality. Did you try applying a vray material to a box and add a vray light to the scene and then render with vray Next? Does it render? Similarly, if you assign a standard material to a box and render with the scanline does it render?
What do you mean nothing changes? Do you mean that the material editor is still showing black squares? If you switch to ART or Arnold with a vray material in the material editor assigned to an object in the scene you should get error messages indicating that the vray material is not supported. F i choose v-ray next or v-ray gpu, nothing changes.
