XBEE S2 with Arduino compatible XBEE shield V03 or XBEE Explorer Board?

I am new to XBEE's. I need to monitor the person's intrusion of a room using PIR sensor in XBEE. Before i start this, i have went through tutorials and forums related to XBEE. All are using XBEE explorer to mount the XBEE modules with arduino board.

Now my question is, which is convenient to use, to transmit and receive the data using XBEE S2 (either to use XBEE shields to mount over arduino or to use XBEE explorer boards)?