为10k +用户保存用户数据的最佳方法

I need to build an app for Facebook in which I am targeting around 10k users. And I need a data storage technique that would be simple and efficient enough for implementation. How do I decide upon what storage option I need to choose? Should I go for a MySQL database? Or an XML approach or JSONs? Or is there any other storage feature I am unaware of? Please help me decide. I need to build an app for Facebook in which I