The Aztec nation has the Jaguar as their unique unit (replacing the Swordsman). The advantages over Swordsman, however, are not so obvious. On one side, iron is not required and Jungle defense is increased by 25% (along with +10% City attack ability, common for swordsman). On the other hand the melee unit is actually WEAKER than swordsman (strength of 5 instead of 6), making it particularly vulnerable against the Axeman. Since you have no choice but have Jaguars instead of Swordsmen, study Iron working as soon as possible. Yet again, it is advised to progress to Maceman (discovering Civil Service and Machinery) as the unit is far more powerful.
The starting technologies are Mysticism and Hunting, meaning it would be wise to discover Polytheism or Meditation (founding Hinduism and Buddhism respectively) right away, and afterwards turn to Masonry, Archery and Animal Husbandry.
The civilization has only 1 leader – Montezuma.