The Molotov Plan is pretty straightforward. While the Marshall Plan was, in part, created to stop the spread of communism, the Molotov Plan was there to encourage it. Money from the Soviet Union could be used to prop up nascent communist states in a similar way that the money from the Marshall Plan was attempting to rebuild western-style democracies.

In terms of which one was more successful, look at the list of Molotov Plan countries. Not a single one of them is still communist. However, the countries the United States helped out are doing great and are among our most loyal allies.