Visa on travelling to Beijing, China

Two of my senior colleagues plan on travelling to Beijing next month (April) for a site visit of the conference facilities. They will be there for 2 days only before travelling to another country. They were planning on applying for a business one but someone suggested they apply for a 72-hour transit since they'll be there for only 2 days.

Which kind of it should they apply for and what documents will they need to provide when they submit their application?