@David Schnider gave a good rundown of the B-corp model. It's worth pointing out that establishing as a B-corp shouldn't, as a rule, be a PR undertaking. The discerning, socially conscious consumer will see right through it.
If you want your primary focus to be on generating revenue, the externalized costs be damned, then you're probably better off using a traditional LLC or some other convention. But if you want your company to prioritize fair labor practices, ecological sustainability, and community engagement, perhaps B-corp is your model.
If you're considering alternative models that may serve broader a social mission - in addition to securing your company's financial position - it may also be worth considering setting up as a cooperative, which may take the ideas behind the B-corp to higher level, including the integration of democratic processes that involve your stakeholders (vs. shareholders). Primary stakeholders will be defined by the type of cooperative (e.g. employee/worker-owned, consumer, producer, purchasing, multi-stakeholder, etc.).