Do I need to apply for a business visa or work visa for not more than 6 months stay in Beijing?

Hi, I am required by my employer to take a long stay for business in Beijing for no more than 6 months. I will not be employed by a chinese company but I will need to leave and return to the country multiple times during my stay (at least 3). i will also be bringing my wife and young son with me.

It appears the visa options are business (F-visa) or work (z-visa)? can anyone offer any help or suggestion on which would be best for my situation and include my family?
Thanks
Pete