The US green card allows you to enter and permanently live in the country. Typically, you can renew the green card as long as you want to live in the US initially for 5 years and then, every 10 years. The work visa on the other hand, only allows you to enter and work for a specific set of years in the US ranging from one to three years at a time. To obtain a work visa, an employer must file a petition for the beneficiary (employee) by offering a job and demonstrating it can pay the salary of the employee. Further, a work visa may be renewed if an employer wants to keep an employee working for him.