Generally doesn't make any difference. Depends what do you prefer. But at least all the examples from Autodesk are written with C# or VB, but not with C++ CLI. If you need to use some native C++ libraries, then it migh be reasonable to use C++ CLI. Although one drawback for C++ CLI is that VS 2010 doesn't support intellisense for it. Hopefully soon. Though there are proper third party softer for fixing that.