Aztecs had individual advancement based on military ability. Incas had little social mobility because the Incans had a totalitarian government, in order to keep control over people, the leader had to limit their mobility.
The Incas were a gentler people, whose accomplishments lay in other fields. For instance they had an excellent system of roads and a very adept messenger service. This helped them maintain order in the largest empire in the Americas. The Aztecs did have a system of courts.
The Maya were native people of Mexico and Central America, while Aztec covered most of northern Mesoamerica between c. 1345 and 1521 CE, whereas Inca flourished in ancient Peru between c. 1400 and 1533 CE and extended across western South America.
-Astolfo