KJW out of the box is probably better (the "father" of airsoft, Tanio Koba had a hand in helping to design the KJ M4), but if the WE is Open Bolt version and you're willing to dump at least $400-500 of RATech parts into it (NPAS kit is definitely needed, and everything else after that is pretty much reinforced/durability parts) you can have a solid GBBR.
Also VFC has some new GBBR's coming out for 2012. Maybe you should wait for them if any of the retailers get their hands on them. They'll probably cost an arm and a leg though. I know the old VFC GBBR's did at least (but also partly because they were a bit rare to find landed in Canada back then as well).
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE