Among the many accounting software packages such as excel, peachtree etc, which one is best to use both for the benefit of business and accountant?

The diversity in accounting applications is because people have different needs based on business size and reporting scale. No one can answer this question for you. Only you can decide. My advice would be to make a list of your needs according to priority then start trials and during the process you shall know what is best for you and your business in terms of usability and flexability.