Yes, Calvin Coolidge did a lot for the United States, because he helped the United States into an era of a good economy. Coolidge didn't boast about his achievements, but on the sidelines, he made the economy more free so that business could prosper. Coolidge's leadership put people to work and kept America at peace. For these reasons he was the best president ever.
No knock on Calvin Coolidge, he did many great things during his presidency. However, there are several other presidents who would rank higher than him, even if there is no real number one. George Washington, Abraham Lincoln, the Roosevelts, all had a huge impact on America. Barack Obama also rates above Coolidge.
It is a bit oversimplifying to consider any one president the best president ever. The fact that the great depression happened almost immediately after him is especially not a cause to deem him as even one of our better presidents. There were other presidents that caused more social change and made important strides in American history.
Coolidge as VP took the office of president on the sudden death of Warren Harding and was elected into a second term. He was an advocate for smaller government and the middle class. He was able to restore confidence in the presidency after years of scandal but he was not the best president in history.