I liked the numerous factions in Fallout New Vegas vying for power. You've got at least 5 main ones but really, they're all flawed and I would have cherry-picked bits of each to make my own.
You've got the New California Republic which is this big bloated bureaucracy that throws its weight around but ends up fucking itself by stretching its resources too thin. It's heads are also corrupt and the soldiers don't always have the training to make the right decisions or the equipment to carry out their orders. They are the one I side with most frequently however, because all things considered they do at least give the pretense of trying to do the most good.
Then there's Caesar's Legion, led by a fanatical dictator who considers women nothing but slaves and whose warriors are suicidally loyal to their leader who has basically inducted multiple degenerate tribes into becoming his legion, and then kidnapping any male children to train as the next generation of warriors. Virtually nothing redeemable about them apart from their tenacity and effectiveness when they set their minds to something.
The Brotherhood of Steel, at least the West Coast version, made me sick. Cowards hiding away in a bunker just eking out a living because they refused to adapt, with the singleminded cause of amassing technology and keeping it out of the hands of others. I couldn't think of a more selfish or pointless goal. The Washington D.C. Brotherhood (that had a faction splinter off because part of them were trying to stick to the ideals more in line with those on the West Coast) were humanitarians, and had more balls than a stadium. I really dug them, but the closest thing to them in Nevada was...
The Followers of the Apocalypse. Really stupid name, made them sound suicidal but hey, they do good works. Peacenik types, humanitarians, concerned more with education and medicine, these guys I really dug, but they weren't ambitious in their expansion efforts and that was sad because they deserved to be the ones holding the power. I would really have liked to support them in either expanding their operations or making one of the other factions fold into them and increase their power that way.
Then there's the unaffiliated Super Mutants. Most of them, the ones that weren't brain-addled by using stealth technology, were content to be peaceful with humans, or simply isolate themselves to avoid any conflict due to murky past relations. The ones that had a good head on their shoulders would have made great leaders in any of the factions but kept mostly apart. I respected that due to the animosity some people can't get over. Same thing with Ghouls, irradiated humans who look like zombies but still, in most cases, retain their intelligence.
Franky I'd have liked the option to recruit people into a brand-new faction that strives primarily towards the ideals of the Followers but which has different branches that focus on multiple objectives. The NCR soldiers, which would now include Super Mutants and Ghouls as major parts of their platoons, would be in charge of exploration and expansion of territory. The mutants and ghouls' immunity to things like radiation would be essential for exploring places like caves and abandoned facilities, but the humans could still help fight against hostile wildlife.
The Brotherhood could be put in charge of manufacture and study of technology (not just weapons which is their priority) and the acquisition of pre-war books and archives and the like, which they do already. But there would be an emphasis on sharing and teaching of how to use power armor which is a jealously guarded secret they seem to like.
If Caesar dies, as is said, his legion would quickly fall to anarchy. Those surviving would be ideal to have as security for any headquarters set up as they'll fight to the last man, and they're great recruiters and trainers, even with animals, although their slaves would have to be liberated first, and the idea behind it would need to be abolished.
Then the Followers would pretty much head the whole thing, making the laws and such due to their compassionate ethics, and of course be in charge of medical treatment and training for others.
Other than that, I thought neither faction in Harry Potter was worth joining. Frankly I disliked the fact that most of the magic users didn't want to share that with Muggles. What kind of shit is that? They're as bad as the pure-blood racists, denying the suffering non-magic populace the cures and conveniences that would make life tolerable for no reasons any more rational or ethical than that of the Voldemort supporters' denigration of them.