Which Bluetooth Module can I use with Arduino Micro/Mini?
I have had good results using the Bluefruit LE UART Friend module from Adafruit with a 32u4 micro Arduino type module, there are only a few pins to connect up to get things going (do remember to follow the instructions to pull the CTS pin to ground).

As per the previous answer it really does depend on what you want to do with it - but this module does Low Energy, can be configured as a "Beacon" and there is a companion App for Android/iOS.