coap server implementation

Hi guys, is there anyone who has tried to implement a CoAP (draft 13) server on an Arduino + Ethernet shield?
I know it is not simple, but in your opinion might be more useful libcoap (which refers to draft 13) : http://libcoap.sourceforge.net/ or other library like GitHub - dgiannakop/Arduino-CoAP at ethernet (which refers to a previous draft)?

Thanks

Daniele