Board Thread:Questions and Answers/@comment-168.221.159.9-20150112144414/@comment-25179062-20150112163842

I think Advent Solace is the best drop boost sphere currently available. It boosts drop of BC 12%, HC 12%, zel 10%, karma 5%, and items 2%. For comparison: Sol Creator boosts BC 15% and Omni Gizmo boosts BC 10% and HC 10%.

The problem is that since you are missing a frozen heart, you would have to wait until the item is made available through another dungeon, which may or may not happen. It is also possible that better drop boost spheres would be available at that time. Personally, if I had abundant zel already, I would probably keep the aspiration stone, just in case.