Rhinoceros 3D would be a good option as it's commonly used amongst architects and can import/export a lot of different file formats. It's also relatively affordable.
Fusion 360 could be interesting as well, personally I have barely used it so I can't comment too much.
If you have no need for CAD, just visualisation, then you can stick to a polygon modeler and use Blender for example (which is completely free).
Tell a bit more what you plan to use the software for.. 'design' is such a blanket word these days.