All light infantry units are strong against heavy infantry units and weak against all defenses.
Marine Squads are your Tier 1 light infantry. They have a medium load capacity and moderate speed but very low attack, defense, and health.
Infiltrator Squads are your Tier 2 light infantry. They have a high load capacity and decent speed but low attack, defense, and health.
Assault Squads are your Tier 3 light infantry. They have a very high load capacity, decent speed and power, and moderate attack, defense, and health.
Jet Troopers are your Tier 4 light infantry - the best light infantry you can produce. They have an incredibly high load capacity, Speed, Power, Defense, and Health.