I work with curves a lot going back and forth between Rhino and Blender. I tend to use OBJ, but it’s hacky. On importing, the scene has to have a mesh object in order for the curves to import. They do match the Rhino output. When exporting objs, i export polylines and need to rebuild nurbs curves based on the vertices. The workflow is not completely accurate though.
When i did need completely accurate result, I had to write a small script because the weight wasn’t getting picked up properly by the OBJ importer. This was a few years back at v 2.78, so not sure if there’s been any change with the current OBJ importer.