For metals, tapping is typically the most efficient option because of the strength of the material, but for plastics inserts can often be a great fit.
Xometry technicians use taps or dies to cut or form threads into parts. This works well with machined components, printed metals, and SLS nylon. Tapping is more cost-effective than inserts. For more information regarding the required hole size and depth for your design, please refer to this chart.
Xometry technicians will drill holes to a specific size and insert press-fit brass inserts. Coiled inserts can also be installed using specialized tooling. Inserts tend to be more robust than tapped holes, but they can also be more expensive. Use inserts when screw installation or uninstall may be repeated or higher torque is required. Please see information regarding the required hole size for your design here.