From someone that has both EASA66 and CASA licenses, I would recommend doing the EASA license. However the CASA License is easier to obtain!! (exam wise) CASA are dragging there feet over accepting the EASA license. Currently there is no cross over from CASA license to EASA, so you will have to study all the subjects again!! If you are planning on leaving OZ to work overseas europe, middle east, etc then the EASA license is a must.
Regards
TOJP.