Best items for adult and ancient dragons to attune to?

[Pinjata]

Hey guys,

Dragons live long. I wonder, optimization-wise, what three magic items would dragons seek to attune to them (if necessary) as adult and later as ancient dragons?

So, my questions are:

a) what three magic items up to Very rare magic items are best to equip adult dragon with?
b) what three magic items up to Legendary magic items are best to equip ancient dragon with?

thanks

[JNAProductions]

Ioun Stone of Mastery.
Stone of Good Luck.

[Beelzebubba]

Ring of Elemental Command combined with one of the summoning items would give it an additional damage resistance and control of a pretty strong helper to soak hits for a few rounds.