I am staying in HK for 4 days but want to visit parts of China. Which entry Visa will I need?

While in Hong Kong I plan to visit Macau and cross the border at the railway station to visit a market place a friend has told me about. I also want to go to Lo Wu shopping complex in ShenZhen. Which type will I need to apply for - two entries valid for 3 to 6 months or multiple entries valid for 6 months?
Many thanks for your assitance.