For the techie's out there, this is often a great subject of debate.
Below are three example images, from the real world, from a standalone VR experience using Unity, and from a PC-VR experience built in Unreal Engine (UE).
But it's not all about graphics, one must consider frame rates, interaction capabilities, and SDK plug-ins.
Image 1 - A picture taken from a camera (built in the real world!)
Image 2 - A picture taken from our standalone VR bus (built in unity)
Image 3 - A picture taken from a PC-VR experience (built in UE)
Looks aren't everything, but they do count.
And that's why we use both engines, the key comes down to the best platform for the training module we are creating, which in turn, gives you the best experience.