I want to know which software is best for the designing and simulation purpose. I want to use it commercially.

 

'Best' in what way? Price, accuracy, model availability, updatable, technical support ....... ?
I doubt there's a 'one size fits all'.

 

Simulating what?

 

Can you elaborate on what you mean by using it commercially? Your post is so ambiguous that almost any answer would fit. I think you would agree that it would therefore be a pretty useless response.