I think metal backups in a bank safety deposit box provides the most reliable security. But you've got to pay the monthly rent expense, so it may not be financially feasible for everyone. If you're holding more than $50k worth of Bitcoin, I think it makes sense as you wouldn't need a large box.

Otherwise, two metal devices would be sufficient, I think. One kept locally in your possession, and another held by a trusted family member in another state or geographic area.

If you're worried about your seed being in someone else's possession, you could get one of those Graphene plate systems that uses two plates that can't be read with only one plate.