- Archers: High of collateral damage, good vs Javelineers, high withdraw chance, can defend cities.
- Javelineers: Very low collateral damage, good vs Cavalry & Heavy, low withdraw chance.
- Catapults: Low collateral damage, good at reducing city defenses.
- Fire Catapult: Extremely high collateral damage vs cities, bad a reducing city defenses.
- Cavalry: Good vs Medium, horrible at city defense, bad at city attack.
- Chariots: Good vs Medium & Skirmishers, horrible at city defense, bad at city attack.
- Horse Archers: Low collateral damage, very high withdraw chance, horrible at city defense, bad at city attack.
- Mounted Javelineers: Very low collateral damage, good vs Heavy & Cavalry, horrible at city defense, bad at city attack.
- Medium: Good at city attack.
- Heavy: Good vs Archers, can defend cities.
Here is a screenshot from the Civilopedia, listing most of the units:
Here is an early design document listing the upgrade path of the units, which is still basically the same:
