What Graphical Only 3D Format Do You Use?

Well, edrawings works pretty good and gives the best visual fidelity without providing goemetry. From there, the person you're sending it to can export it to STL if they want to bring it into Max or Blender or something

You can write the files straight to STL-which most programs can read in.

I typically send STEP files, but it really depends on what software your vendor/customer has.  Many programs are limited in the filetypes that they are able to import, so you may have to work with them to find something that works.  Try exorting your different options, then import them back into SW to see how they turn out (sometimes you will get errors in the conversion process.)

You have several options.

Save as the assy to a part with the Exterior faces or Exterior components option.

On the newly saved part you could use the Defeature tool to further reducte details.

From that I would use either an eDrawing or 3D PDF file format.

If your client needs to load the part/assy into another 3D program to check fit, clearances, etc, then Parasolid, STP or IGS  formats should suffice.