Noramlly, perople will say L/C (Letter of Credit) is the safest method. However, it depends on many issues and critira. Such as the total amount of the order, the quality of the products and etc.
For my company, most probably we use T/T and L/C for the payment. For the BIG amount, we will select L/C as both our customer and us will take care more about it. Otherwise, we will select T/T as the handling cost is very small.