can you tell me more about the three factions of the Shell?

Really high level summary!

Family Culture: Agricultural communalists living in politically divided city-states. Families are sort of like communes. They have a single industry, product or service that they make, and they're VERY tight knit.
Most people in Family culture live under the Federal Family, who's trying and mostly failing to turn the Heartland into some kind of nation-state.

Duhr: The city of debt. A mercantilist, individualist society that's fixated on accounting for the flow of spiritual energy through the world. Basically a huge, anarchist, and "spiritually capitalist" city-state which exports a lot of wood and metal.

The Temple States: Caste communalists, ruled by a theoretically technocratic elite. Once a single empire, now a bunch of bickering successor states. The richest, oldest, most technologically sophisticated part of The Shell.

That's cool
I know the answer is probably none of them, but who would be the "good guys" in this case?

Family culture is the "nicest" for most people,. They have a huge focus on providing for people's social and emotional needs. If you're "in" Family culture, you can expect lifelong and unconditional love and social support. But it has out-groups who can be marginalized in nasty ways. While they're not *religious*, they care a lot about social orthodoxy. Which is good when a lot of that is about treating people well, but there are also shitty elements to it. They believe, like most lizards, that their way is the best and only "right" way.

Duhr has the most systemic suffering and poverty compared to other cultures-- Duhr has weird ideas about personal responsibility for poverty and bad living situations, (compared to other cultures which tend to see providing for people's needs as more of a collective responsibility). However, people also have the most agency in Duhr. In Duhr you can separate yourself from relationships more easily. You could... pick a career, and maybe change it midway through life, which isn't really a thing in the Temple states OR Family culture. Duhr tends to appeal to people who are marginalized in the shell's other cultures.

The Temple States is authoritarian, elitist, and moralistic/religious but they're also the richest and the best at avoiding big marginalized out-groups. There really isn't much poverty or material deprivation in the Temple States, there's a high standard of education, and the powers that be genuinely try to find a place for everyone within their society. So long as you accept having no real political power.

fair enough