I assume you mean the GBBR version, since G&P makes both a GBBR and AEG CAR-15.
Honestly both the WE and WA (what the G&P GBBR's are based off of) systems have their ups and downs, but personally I am biased against WE. I would say go for the CAR-15, but make sure you get the version that has steel internals, not the WOC-X aluminum internals one.