First, you need know what is the reading distance required for RFID reader, and then, what is the reading speed you want, Secondly, you need to know what kinds of communication interface you want, like RS485 or RJ45? Thirdly, you need to know what type RFID reader you want? RFID fixed reader or RFID handheld reader?
Thus, you can know the RFID reader hardware selection. 
