1

I am an artist and I have created some 2D work which I would like printed 3D. I use Mac which is the best program to save this work from and which format?

2

It depends of what you want to do with it. 2D is 2D. You can extrude 2D to a 3D shape, you can do this with many programs. For example 123D design (free), save your 2D to .SVG and import it in 123D Design. If you use (one of the latest) Photoshop you can also create 3D files.

Most 3D printers work with .STL or .OBJ files.