For a graphic design company based in a single office the best computing device would be a laptop with a tablet peripheral for drawing on certain software like Photoshop. This would be the cheapest option and the most space efficient so that there can be more room in the office.

For a travelling sales person the best choice would be a tablet computer, so that it's very portable but has the ability to attach peripherals like keyboards. This allows the sales person to easily move around to do their job but can also be used for basic computing in a single place if needed.