I think thatAdamantium is an alloy based on Vibranium and harder than it, but maybe I'm wrong. During Assault on New Olympus, Herc told Wolverine that the chamber they were trying to open was made of Adamantine or somthing like that, "like his adamantium but in divine version". So I guess that's the real winner. About Cap Shield, I though it was made from something different than Vibranium, and that Adamantium was the result of science guys trying to replicate itwithout successor at least I remember reading something similar. In fact when Ironfist was brainwashed by Osborn Thunderbolts and had a nightmare, he took the shield and threw it to Wolverine's head and it opened the skull. And if Cap shield has bee destroyed, I can say at least one time Wolverine claws were broken easily: S'ym took one from Wolverine's skeleten on limbo without effort (cracking it, not separating from the articulation) and then threw it to Colossus.