For visiualization of the internal structure of human body, is it best to have computed tomography?

No: It depends upon what you need to visualize. If you need to see the cerebellum, a ct scan doesn't work as well as an mri. If all you need is to look at the liver or kidneys, then an MRI is overkill compared to an easily accessible ultrasound. Plus, ct scans expose you to (unnecessary) radiation. So ask your family physician and radiologist what's the best way to find the information you need.

No: It depends on the region of the body that is to be examined. In some instances, computed tomography is the examination of choice, but in other instances MRI or even ultrasound may be superior. The answer for what test is best is complex and depends on the clinical question being asked.