To the original question: Lightsaber = unstoppable force. Adamantium = immovable object. If you read enough of the background fiction, you'll find there are things that stop lightsabers and things that dent adamantium. Generally the objects or forces they encounter are less sturdy than themselves and so break with only moderate effort. It's only when they encounter something else very strong or tough that it becomes a question. Even if a lightsaber could cut anything if sufficient force were applied, the arm holding the lightsaber will not have infinite strength. Likewise, whatever is hitting the adamantium is not doing so with infinite force (even the Hulk can only punch so hard). I abstain on the grounds that the question is subjective.
To "how do you make adamantium in the first place": I figure it's like making concrete. The things you put in the mixer aren't concrete until they've been stirred together in the right proportions and allowed to harden. After it hardens it's stronger than its components and can't be unmade just by reversing the process. Adamantium is Rule-Of-Coollurgy rather than metallurgy but the same principle should apply.
As to why Wolvie's claws cut through nearly everything, I figure they were made with ridiculously sharp edges, monomolecular or nearly so. Since adamantium is so hard, the claws would never need sharpening. Logan would still have to be strong to push the claws through steel, but have you seen how much muscle there is on that guy?
Bottom line: You're dealing with stuff that doesn't (and, arguably, cannot) exist so throwing science at it will take you only so far. It comes down to opinion.
