which is the most common and best software for rendering.?

"Best" is a subjective term. And some rendering software may be "better" at certain tasks than others.

I personally like Keyshot. But I've seem excellent renderings out of Rhino, SOLIDWORKS, Modo, 3D Studio Max, Cinema 4D, Maxwell, and other rendering programs.

The important thing is to look for a program that is easy for you to use. I tried for years to make good renderings in the products included with SOLIDWORKS, but they never looked good. I feel that I am finally getting good results with Keyshot.

Another factor is what you plan to render. Keyshot is great for products, but I don't believe it is great at say architecture scenes. It is not bad, but you may find other programs which may be better suited for such scenes.

i think keyshot is the best software as far as product rendering is concerned
it will give realistic images and animations
I am very much satisfied with results

Apart from KeyShot.
Try Rhino & Solidworks Visualize too.
However you will be satisfied in Keyshot about Easy interface and Realistic outcomes.
Can try GPU rendering for better performance.
Its my personal opinion after using these atleast 3 years or more.

Keyshot is best software for rendering