Humans (Apocalypse)
Humans will probably be the mainstay of your forces. They usually start out with very good physical skills, they level up in them quite quickly, with these soldiers obtaining amazing accuracy and stamina levels within a very short period of time. The only true problem with human forces are their poor psionic skills. These troops tend to be very susceptible to psionics when facing off against Micronoid Aggregates and Psimorphs. Even when maxed, their own psi skills are completely ineffective except against some anthropods. Otherwise, these troopers can go through anything very quickly. With the proper firepower, they will surpass all of your other troops.
You can train human agents. This can only be done if the base of operations at which they are staying has a Training Area or a Psi-Gym.