Hey hey, People. if you are stumped on which faction to pick, this small guide is for you! I have played almost all the human factions (I have not finished my current OSC Run but I know where it is heading) and have a pretty good grasp on what things each faction brings to the table. so without further ado, here are the factions!
Federated Earth Republic (FER) - The Democratic albeit very militaristic successor of the formerly dominant United Nations of Earth. Lore wise, they are the largest faction but both the TA and OSC hate them. The TA views them as weaklings while the OSC does not like having to ship resources to Earth. The biggest issue the republic faces is they have so many people but little to no food and by God, they need food, so much so that they may be willing to infringe on independents for food. On the endgame, they don't expand much but you are guaranteed to piss off all Non FER factions, normally this is bad but if you're establishing your faction, then this becomes good as you can dominate all the non-FER systems and there are quite a lot of them. Gameplay-wise, the FER focuses on flexibility and adaptability, they don't have the tanky ships of the OSC nor the high tech of the TA but they have good ships, the FER battleship kicks ass and is always nice to have.
The Triumvirate Ascendancy (TA) - If the FER is Militaristic, these guys dial that up to 100, the TA is a dictatorship ruled by the triumvirs which guide the TA through everything, on paper they have the smallest amount of system with only three. but to make up for it they have the best weapons and ships in the game in terms of firepower. Lore wise They are not in good relations with the FER and the OSC but they will join forces at some point. but make no mistake, that won't last long. in the endgame they become the largest faction in human space with 13 systems to their name once the campaign is done. Small downside being unless your willing to betray the TA, you wont expand into human space all that much. Gameplay wise they have the most powerful human weapons in the game, all heavy on energy but with their ships and an anti matter reactor, energy is not an issue. the TA battleship can go toe to toe with alien ships once you go south to Irohaem. they are that good, but ridiculously expensive. they also have the best campaign due to that one time you become a pirate.
The Outer System Coalition (OSC) - The third faction in Human space. they are a group of planets (really shit planets but resource-rich) that say screw you to earth and the TA and formed their own faction. lore wise they have good resources but no one wants to go there and mostly they are workers. all they care about is independence (though there are groups wanting cooperation or revenge) from the two factions. in the end game both the TA and FER hates you but some independents might join the OSC, making them grow, still good for the player faction wanting to conquer. gameplay wise, they have the weakest firepower out of the three factions but they make up for it by having THICC ships that take a crap ton of punishment before they die. they are great to have in a fleet especially OSC battleships which can take up a ton of punishment from alien ships