#second age

The Falathrim under Círdan, who were closely connected to both Nargothrond and the Fingolfinian strongholds in Mithrim

The Northern Sindar of Hithlum, who were vassals of Fingolfin and Fingon (under no known singular leader)

And regardless of whether you accept Gil-Galad son of Fingon or Gil-Galad son of Orodreth, it's very likely that as the seat of the High King of the Noldor, Balar was also home to the Noldorin remnants of Fingon's host that didn't (presumably) get swept up into the Fëanorian forces following the Nirnaeth Arnoediad, which at that point would have included the remnants of the Aegnor and Angrod's forces from Dorthonion, Fingolfin's forces, and Fingon's own forces.

Amon Ereb, which I think is broadly aligned with "Balar" on the "Balar vs Sirion" scale, but probably uncomfortably so (especially after the 2nd and 3rd Kinslayings), was of course host to the remnants of the Noldorin and Sindarin forces of Himlad/Himring/Thargelion, plus a large contingent of the Northern Sindar who were outriders in the plains and highlands of the northeast. The Green-elves of Ossiriand were likely split between the two camps or purposefully neutral.

How does this map onto the political landscape of the 2nd / 3rd Ages? The elven realms east of the Misty Mountains (the Greenwood and Lothlorien) are implied to have a distinctly different character from those west of the Misty Mountains (Eregion, Lindon, and Imladris) despite both being noted to have Noldor & Sindar mixing.

IMO the easiest way to reconcile this is to assume that east of the Misty Mountains, "Sirion" prevails-- this is where the "Sindar princes of the Silvan elves" (Celeborn and Oropher->Thranduil) rule, and most Noldor present are largely Gondolidrim or from Nargothrond. Any Green-elves who were incredibly opposed to the rule of the Noldor likely migrated in this direction to their ancestral homes near the Anduin.

West of the Misty Mountains, on the other hand, I assume that "Balar" largely prevails-- this is where Gil-Galad rules, and where the Sindar of Hithlum, the Falas, and the northern plains --and the remaining Fingolfinian, Dorthonion, Fëanorion Noldor, and some fraction of the Gondolidrim-- spread out in complex ways between Lindon (which encompasses remnants of both Ossiriand and Thargelion), Eregion, and Imladris. It's likely that Harlindon specifically-- one of the last remmants of Ossiriand-- is home to a large body of Green-elves who will not be parted from their homes, but who may have wildly varying opinions on Noldorin rule and ... the 1st Age in general.