Start with the toolchain that consumes the file
The right format depends on the data you need to exchange and the applications that will use it. A robot description, an assembled environment and a simulator-specific model have overlapping requirements, but they are not interchangeable deliverables.
What each format is used for
USD represents and composes scene content. It is useful for assembling environments and carrying supported geometry, materials and physical data. See the OpenUSD introduction.
URDF is used in ROS-oriented robot-description workflows. The urdfdom project provides the parser and model representation. Confirm the needs of each downstream tool, including any extensions it expects.
MJCF is MuJoCo's model-description format. The MuJoCo modeling documentation explains how model elements are interpreted and compiled for that simulator.
These are roles, not a ranking of formats. A project may use more than one while maintaining a clear source of truth for each representation.
Treat conversion as a mapping to inspect
List the data that must survive conversion before choosing a tool: geometry, frame relationships, joint definitions, physical values, materials and dependency paths. Then inspect the actual result in the receiving application.
Do not assume that a property with a similar name has identical units, defaults or runtime behavior. Keep conversion settings and tool versions with the output. Run a small representative interaction before converting a large collection.
Ask for a concrete delivery definition
A useful request specifies:
- The receiving simulator and version.
- Which file is authoritative and which outputs are derived.
- The robot or asset components that must remain editable.
- Required joints, contact behavior and label conventions.
- Package dependencies and a repeatable acceptance test.
simgenerator's AI generation produces USD. That does not imply that every generated asset includes URDF or MJCF exports. Review the actual package specifications in the library and confirm additional format requirements when scoping a custom project.
Read the USD quickstart before importing a package, and the conversion guide for the distinction between file conversion and physical authoring.