If you are shipping within U.S., my personal preference would be US Priority Mail with Insurance, but U.S. First Class Registered Mail with Insurance is also an option and less expensive (I just hate the tape protocol required for domestic registered mail parcels).
Do a google. I think fed ex limit on jewelry is $500.
The best way is to send insured registered mail but it’s sooooo slow, like suppeeeerrrrrr slow.
A lot of couriers limit jewelry as an exception. So you might get 2k insurance for no jewelry but if it’s jewelry then its $500. I usually say it’s 2 pair of prescription glasses lol. I don’t know if that helps anything in the end…
If I’m sending a stone to say David Klass, I buy a label from him so he can use his company insurance on the package.