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.