Hi skan. I'm afraid the question "What about STL?" belies a fundamental misunderstanding about CAD systems in general and this debate in particular. Sorry, I don't want to sound patronising but there is very clear division between nurbs based CAD and mesh files of all types. STL is a mesh, originally developed for Rapid Prototyping (Now called additive manufacturing or miss-named 3D printing) machines. Mesh files are also common amongst programmes designed for visuals, games and on-screen applications but all proper CAD software, especially parametric systems primarily work with nurbs. The 2D equivalent is the difference between bitmap images and vector based graphics or between a scanned document and an editable text file. Both have their uses and limitations but they are not interchangeable.
STEP data is the best, since it retain the Solide geometry even after translation, IGES good for sufarce data translation