Close relatives of US citizens & highly skilled workers get the best chance of finding permanent legal residence in the United States. When people talk of the easiest way to get a US green card, they usually use the fastests or at least ambitious way to become a legal resident (LPR) in the USA.
In the context of modern American immigration, the waiting period for many US green card applicants can be 10 years or more. However, for some lucky people, this wait can last several week.
Of course, what is “easy” relies in part on what you are entitled to. Existing family relationships with US citizens or permanent residents can make immigrations uncomfortable for most people. Work offers work for others.