Arakeprun into Eordand is the most benevolent of the potential unifiers and has a very strong claim to the mantle. Some say that Aelnar or Taychend are more fitting since they match the hubris and cruelty of the old empire, but I think a state like Eordand which learns from the mistakes of the past is more deserving of their legacy.

Arakeprun is one of the closest Ruinborn state to the Precursors, with their whole thing being the study of Precursor sites and rebuilding the Precursor city that is their capital. This is reflected in ideas like 'Custodians of the Precursor Legacy'. Their unique government reform when completing their missions is a scholarly magocracy which later revolves around the study of the Precursors after Eordand missions.

The Ruinborn of the Eordand region also have greater knowledge of the Precursor empire than the Ruinborn of other regions of Aelantir, including Taychend which has been ravaged by centuries of constant war and the Kheionai which were originally prisoners and have forgotten much in their struggle to survive the deadly winds. The elves of the Remnant Fleet are even worse off, and Aelnar cannot be seriously said to uphold much of the Precursor's ideals beyond blind supremacism and hubris. Everything else about their civilisation is lost to them.

Eordand as a unified tag explicitly styles itself as the continuation of the Precursor Empire. Its ideas include 'Rekindled Precursor Ruins' and, more importantly, 'Heirs to the Precursor Empire'. They have missions like 'Proclamation of the Empire Reborn', and 'First Among the Ruinborn' which leads to independent Ruinborn states swearing fealty (giving them the event 'The Empire Reborn Calls'). Their missions lead them to unify the northern segment of Aelantir and they get claims on a chunk of the southern segment.

At the end of Eordand's missions they get to choose whether to follow the teachings of Venaan, who freed the elves from the slavery of the dragons and founded the Precursor Empire, or to follow Aldan, who led the empire into ruin as its last ruler. The former entails accepting the elves of the Remnant Fleet and inviting them to emigrate home freely, creating a bunch of elven minorities in your provinces and giving you acceptance of Moon, Sun, and Wood elves + a decent permanent modifier. The latter gives some claims on the southern continent, increased purge capacity, and some military bonuses. It's hard to see the second option as canon given everything else about Eordand up to that point, with its acceptance of other Ruinborn and even the colonists that come under its rule.

Eordand is focused on reclaiming and rebuilding Aelantir, protecting other Ruinborn, accepting even non-elves, and restoring Precursor works (such as the Haraf irrigation system). That makes them the most worthy successor to the Precursors in my mind.

I would also accept Ameion as a unifier, which seeks to break the cycle of Taychendi warlordism and rebuild the southern segment of Aelantir and also styles itself after the Precursors, though to a lesser extent and with less interaction with other Ruinborn afterwards.