Eixo Monumental is the world's largest avenue when measured from one side to the other, including the midsection's esplanada. However it has less car lanes then 9 de Julio.   

 Difference between "Esplanada dos Ministérios" and "Eixo Monumental" 

As far as I know Brasília, the name "Esplanada dos Ministérios" (Ministries Esplanada) is used only to the first section of the Eixo Monumental, where the ministries are located. The names are not interchangeable.