Agents (Apocalypse)
Overview
Your agents are your lifeblood when it comes to close combat engagements with the enemy. Agents are highly adaptable soldiers trained in all the arts of - well - urban warfare. They come in all races, creeds colours and shapes. X-Com does not discriminate and is an equal opportunity employer. Come one, come all, if you can survive the night - or your first mission - then you will go far in the organisation.
The Races
Humans
Humans are fundamental trooper material. They will probably make up the largest of your soldier population. They start with strong to average abilities and can become very skilled soldiers fairly quickly. The only thing that humans lack are good psionic skills. Their starting statistics tend to vary widely. Be sure to screen those otherwise superb recruits for psi-def or bravery deficiencies!
Pros: Wide availability of recruits means you rarely run out of human agents. Relatively fast statistical improvement means that even subpar agents can increase to respectable levels, with time.
Cons: Psionics, morale, brainsucking. Humans are also fragile.
Recruitment: You can't really lose recruiting options with humans, but it's generally a good idea to keep people in your good books anyway.
Hybrids
Hybrids are the result of a crossing between humans and sectoids. No one's certain why they end up bald and with ridges on their head, but they take on the qualities of their sectoid bretheren. They are mentally powerful while frail in the flesh. However, being part human, they have the potential to become as powerful as their pure human cousins on top of their psionic skills. As a race, they start their service life very poorly. But as they mature, they can become incredibly powerful, making them good long-term investments. The only problem is keeping them alive that long whilst still exercising their powers.
Pros: Psionic capabilities are useful, but suffer from drawbacks in Apocalypse.
Cons: Pretty much the same as human troopers, though often even more fragile. However, due to the psionic "nerf" (they only function on a line-of-sight basis, at least for untrained psions) hybrids are less effective than they could be.
Recruitment: You must be on good terms with Mutant Alliance to ensure a healthy quantity of Hybrid recruits.
Androids
The androids are the oddball of the three species that are employed by X-Com. The androids make a valiant attempt to eke out their virtual existance in the physical world by doing their best and taking as much advantage of their cybernetic bodies as they can. Unfortunately, they are not able to improve physically in any way or form. While this may sound like a big detriment at first, they should not be underestimated for this one fact as they begin their life of service as combat hardened soldiers. They are highly dependable and very durable (and some with a more macabre out look on life would say, expendable). Androids can go so far as becoming body shields to protect their other training comrades, as they need not be in top form at the end of the day to utilise any training facilities. As androids are mechanical in nature, they are mostly ignored in the field of psionics, which means they cannot use it, but are also immune to it.
Androids make excellent shock troopers and are ideal for sending into UFOs first - not due to their expendability, but due to their immunity to brainsucking and psionics. Androids are also highly capable in combat and often start off with superior statistics. Not only that, but their starting morale is usually 80 or higher, making them unshakeable in combat except in the face of superior numbers and weaponry. Contrary to popular belief, Androids reportedly do gain experience and improve their statistics, but this rate is incredibly slow - androids may not experience any increase until well towards the end of a campaign even if they have been with it from the start.
Pros: Good starting stats - especially health and morale. A shot that could kill a human may merely critically wound an android.
Cons: No, or negligable, stat progression. No psionic capability is a double-edged knife.
Recruitment: Few or no android recruits will be available if you don't keep S.E.L.F. - the Sentient Engine Liberation Front - happy.
Though most X-Com commanders end up utilising humans in the majority because they are the most well rounded race, a good mix of Hybrids and Androids does allow for different tactical advantages that are normally not available to a team consisting entirely of one race.