it was a writer's mistake and also a bui mix up that stated cap's shield was vibranium and adamantium composite.. in actuality it is still just an unknown steel alloy and vibranium..
anyways............
Adamantium also has a good lvl of kinetic absorption as stated by wolverine... Vibranium just happens to be better at it, not only does it absorb kinetic energy but also various energy types as well as store it. but it is still weaker then adamantium and it also has limits to how much energy it can safely absorb...
Cap's shield is the exception b/c it is not just Vibranium but a completely unique composite metal...
but to answer the question Adamantium is the strongest of them two. Vibranium has bn shredded by bone claws from wolverine to sabretooth.. both have damaged it.. wolverine has done it on cardiac vibranium armor and sabretooth on both Black panther's vibe suit and Mavericks vibranium armor..
also ironfist has ripped and torn black panther's vibe suit with blunt force damage..
also Mr. Fantastic has severely damaged Klaws vibe Claw cracking the outer shell with a weapon blast.
Vibranium has bn shown on panel damaged repeatedly on panel prior to hudlin's run and well after. Hudlin's Run just made vibranium look cooler.