The rule is almost embarrassingly simple: name the relationship.
Anything that names the specific relationship — Gammy, Nana, Grandad — outperforms a more expensive generic gift, because it cannot have been bought for anyone else. This is the one category where personalisation is not a nice extra but the entire point.
A generic "Best Grandma" mug could have come from any shop and been given by any grandchild. The specific word a family actually uses turns the same object into a record of who gave it. Grandparents keep the second kind.
Editor's pickA mug beats almost anything in this category, because it is picked up every single morning. Ornaments beat photo frames because they come out once a year and carry the memory of the year they arrived.

A first Christmas ornament, dated, is the standard here for a reason — it becomes the item that comes out of the box first every December, and the date does the emotional work without anyone having to say anything.

$12.95