Here is sort of a rundown on what each faction's fluff is like,
Pan-O: The richest faction. Their soldiers have the best equipment money can buy. They're the Hyper-power of the sphere, the best TAGs and best Heavy Infantry. Lots of Knights too. They rely on their gear to get through sticky situations, doctors and hackers aren't the best but they have good gear. Not a ton of tricks, mostly straightforward in playstyle.
Yu Jing: Like heavy infantry? Yu Jing has lots of heavy infantry. Lots of melee specialists too. They also totally do NOT have Ninjas, ninjas are a complete Myth. The Emperor would NEVER sanction an organization of remorseless killers with no oversight, absolutely never

They also do NOT send criminals into battle with explosive collars, that would be illegal, cruel, and unusual.
Nomads: Lots of tricks, best hacking faction. Solid all around units. Faction of smugglers, lawbreakers, and all around scum and villiany. Also cat girls.
Haqq: A faction of light infantry, and the best doctors. Slightly less techy than the other main factions.
ALEPH: A faction of super post-human cyborgs. Soldiers are expensive, have excellent gear. Lots of characters(heroes of greek myth recreated)
Combined Army: A consortium of alien races in service to an artificial Alien Intelligence which is searching for the key to enlightenment. You got robots, space klingon gorillas, and space frogs who want to breed and populate the galaxy with their spawn. Also kinda have a "We are the Borg, you will be assimilated" thing going on. Can mind control many of the other faction's units because people put computer chips in their heads now.
Tohaa: Artichoke face aliens who have symbiotic armor and weaponry which is allergic to fire. Hate the Combined Army and are desperately trying to use humans as a meat shield for their relentless advance across the galaxy.
Ariadna: Low tech human faction. Make up for it with lots of dirty tricks like hiding in bushes and sniping people with the rough equivalent of depleted Uranium bullets. Or throwing mind controlled dog aliens and human hybrid werewolves at people. Faction comes in Russian, French, Scottish, and 'Murica! flavors. Little to no hacking, and the vast majority of units are unhackable.