Which you choose to kite, kill really depends on your guild. We have done it both ways, but find that when things are going smooth and we can get the brutal chain killed its the least risky.
However, for some reason agro is flakey on the brutal. if it was my choice I would always kite the sapper and the escavator (which we do), and Kite the brutal while the have the necro's dot it into the ground..aka kill it while the rest of the raid kills the warriors and shaman.
I haven't been able to determine what's up with agro on this event, but agro is extremely wacked. The only thing I can think of is raid position, but we haven't tested that yet. Agro is so messed up that I have seen the brutal fixed on a caster who didn't do anything to him and the sks's unloading agro on it with no luck.