In terms of price, futures and spot are the cheapest, but there is a time limit for futures delivery, and spot delivery has the lowest cash ratio.
As mentioned above, you should know the purpose of buying gold. Make money? Then choose futures or spot; Pure preservation is true.
Spot and futures can be traded in the corresponding platform vendors, and physical objects can be purchased in gold shops such as banks and China Gold.
You can also buy physical gold when going abroad. Geographically, South Africa and Dubai are the cheapest.