In infantry you can be either a Medic, Infantry, Commando, Engineer, Jump Trooper, or Commander. Each class has their own special skills and weaknesses however all of them as a team can lead to one power house of an army for either the Titans, Mercs or Collective. Normally they are used as the front line of defense against invaders. Infantry men are the normal Joe blows, but are also one of the best classes. They can have decently destructive weapons and use some pretty good equipment which makes them agile and deadly at the same time.
Medics are weak, but are a big plus to every army.
They have the ability to heal wounded soldiers and summon troops on the battle field which makes them a must have in any platoon. Engineers are also one of the must have characters out there on the battlefield. They can build defenses for a base in order to protect it from attack via turrets and mines. Jump Troopers are weak and used for sniffing out enemies. They have the ability to use any fast moving flying machine out there, including hoverboards which makes them an awfully hard target to shoot.