AGU bottom end is stronger than BAM, only reason BAM has an alright safety margin is as said above, it has a lower compression than the AGU, AUM etc. AGU head is preferred for big turbo conversion over other heads because it's large port which means it should flow better, the VVT stands for nothing unless you want to keep the emissions down which was what it's designed to do - it has no real performance gains except for those who plan to get the VVT attack software which is questionable. There's also no reason why you couldn't run the big port AGU head and swap over AUM or BAM cams and cam chain tensioner over and still have VVT either.
It depends what you mean by which is better, if your going for ~300 bhp BAM, AGU and the weaker AUM bottom end will get you there but obviously the AGU providing bit more reliability. But after that your going to be changing the internals anyway. The only advantage with the BAM is that it's already got the ko4-02x turbo fitted so would be able to make 260-270 which is more than what the k03/s will give, but if your set on 300 then that stands for little too as your either going to have to go for a hybrid or a big turbo in which case changing the internals on would be suggested whatever block your running.
