For a prototype which is expected to drive some interest 3d printing is fine, but print at 0.15 layers and do a couple of runs of sanding combined with filler before applying some paint. The case will look just like a regular finished product. I do this for custom projects where I want a perfect finish and/or show-off prototypes.
The layering is really annoying for some people.
For a final product, depending on the sale numbers, injection molding might be the only option. SLS and MJF give a very nice result, but the price range where they're economically viable is very narrow.