[Ibrîniðilpathânezel]

While the argument for Ecthelion is strong, the notion of it being Tuor's brings to mind a potentially interesting lineage. What if Tuor, having come by it among Turgon's gear, gave it to Eärendil, who took it with him into the west and used it in his big battle during the War of Wrath? That would be a notable deed, and I could easily see the Valar making sure it was left behind somewhere, knowing it had a destiny in Middle-earth.

Ultimately, though, I think it would have belonged to someone who perished in Gondolin, as both swords were found together and probably got passed along that way. I've long felt that the orcs and other nasties who preserved them did so because of conflicting feelings of fear and greed, wanting to have such precious things, but also wanting to keep them out of circulation. Ecthelion was probably the most famous sword-wielder other than Turgon who died in Gondolin itself, so I think it likely that he was the owner.