Both ERAS and GOF 2.5 started with GOF 1.2 as the basis and GOF derives from COAS. ERAS has been continually updated through 2023 and would be the latest, most current mod based on COAS right now.
ERAS removed much of the fantasy and historically inaccurate ships from GOF, but added many more other ships and characters, one new Pirate colony and other features that don't exist in any other COAS mod. GOF 2.5 removed many ships and much of the AI and other improvements from GOF in an attempt to fix bugs they thought were created by the GOF mod itself. However, the bugs were mostly due to a buggy original engine, so both 2.0 and 2.5 remain a shadow of what the original GOF provided and I believe actually still have their own bugs; I do not update GOF 2.0 or 2.5 and leave them as they stood, but offer them because for some reason, people still want them.
In my opinion, if you want to try GOF, version 1.2 is the best, and 2.0 and 2.5 removed too much of what made GOF "good." But to answer your question, ERAS would be considered the latest and solid COAS mod right now.