9: Vodyani: Find the heretic, destroy a planet zzzzzz

8: Craver; What happened again here? 

7; Horatio; I'm the real Horatio, kill the fake! We killed the fake......the end?

6: Sophons: Ai gone rogue always makes pretty good stories, this one was just average

5:  Unfallen; A good story about self-discovery and growth as a species accustomed to just living by old traditions and afraid of change

4: Lumeris; Many interesting options. Choosing between the families and the feuds that follow; assassinations and business. It's like space scarface. I like how it gets deeper into the families who are the ones that control the lumeris civilization

3: Vaulters:  Nostalgia filled story, quest to find the best character in the endless series.  Looking for Auriga, searching for survivors and more interaction with Isyander than most other faction stories.

2: United Empire; Being able to change your faction completely and see how that transforms the story and gameplay is superb

1: Riftborn: Inverse Lovecraftian horror, very very refreshing to play as an alien that sees our universe as an abomination. The choices you make can really affect the tone of the story

So I still haven't made up my mind on exactly why I have rated each faction's questline as I did, or what the most important elements of a storyline are for me. The two biggest themes so far are 1) a faction being driven forward, its ideals being threatened or tried, and growing as a result - and 2) narration being matched by gameplay impacts. 

I think the worst example of the former is the Sophons quest, who go through an entire AI rebellion and end up with practically the same viewpoint as before (and aren't even particularly bothered in putting it down, which is unlike every AI rebellion story ever), while the best example is the Riftborn, whose questline manages to ask some really existential questions about what it means to be Riftborn - whether they even are/can be Riftborn in the new universe, whether their old society can survive, and if not, what is a right and fitting replacement. The grim endings fit well with their story. Meanwhile, the Lumeris deserve mention as not really being subject to this at all. I suppose you could argue that 'how their society responds to the craziness of an entire galaxy to economically expand into' is a fitting challenge for their culture, but it doesn't offer anything that strikes at the heart of what the Lumeris think it means to be Lumeris. Instead, it's about mafia family maneuvering and drama, and is one of the most inwardly-facing stories here - which in my estimation is, in all cases but one, not a good thing.

Horatio, the exception, is kind of in its own category - as is fitting. It's not a 'faction' quest at all; it is a story about a personality. And given the subject matter, that suits it perfectly. Horatio bothers himself with thoughts about how 'The We' is to best go about interfacing with the galaxy, but certainly not to the extent that Horatio bothers himself with Horatio. Still, it lacks the pizzaz of the most well-done questlines.

In terms of the latter questline element, I'd say that the United Empire are the clear winners here - from nearly the beginning of the quest you can see how the politics of each choice impacts your empire appropriately, and the keystone decision of the entire questline is unmatched, inventive, and just super cool all around. I haven't finished every branch of their questline, but I can say that in nearly every case the decision you make has a fitting impact on gameplay.

The Vodyani aren't necessarily the worst in this second category, it's just that a good number of their quest choices provide outcomes that feel kind of unrelated. Furthermore, my suspicion is that a larger-than-usual number of choices are not balanced properly against each other, and so it feels like gameplay efficiency drives you to choose one path more often than the other. I would like to see each path for them (every path for each faction's main questline) be both relatively 'balanced' against each other, and also lend itself towards a different playstyle, as further incentive against always choosing one quest option.

Here's a tentative list, ranked in no particular order:

Last: Sophons, Cravers, Vodyani. These aren't too much worse than any other, it's just how I feel to rank them right now.

Mid-tier: Lumeris, Unfallen, Horatio. None of these are bad, but they are less inspiring (they don't draw me in to the story as well) than my favorite questlines. (none of the quests are bad, in my opinion, though most/all could use improvement in some ways)

Best: United Empire, Riftborn, Vaulters. I do wonder if part of my ranking of the Vaulters is nostalgic, but I think that the relatively more recent writing of it is an improvement over those of the first-released factions... for the most part. Were I not including the Vaulters in this list, I would choose the Unfallen as among the first tier of questlines. Their quest is one of the best, lacking only in the narration->gameplay department.

Well, that was wordier than expected. I hope it was a decent read.