I have bought a lot of silver and some gold coins lately. I mostly buy coins where I like the design, and it is a well known series (for example Lunar series by Pert Mint) with not too high mintage. Not rocket science really. I am actually thinking about buying this one:
https://www.apmex.com/product/160183/2017-barbados-1-oz-gold-trident-bu. 49.99 over spot. Cheaper if you pay with BTC though.