i'm no expert but i have heard that POI shift is more prevalent in cans that are the quietest. therefore the surefire can would be louder than a gemtech, aac.
from what i have heard and read, the POI shift is caused by the asymetrical baffle desing but thats what makes them (gemtech, aac) so quiet.
so i guess its up to the operator, what is most important? personally i would like to have both, a really quiet can for a short barrel doing CQB work and a can for a sniping rifle that has little POI shift. that is my goal.
i have a m4 2000 from aac, the only down side is the special flash hider that costs $90 friggin bucks, what crook. the up side of the pricy FH/mount is that its a really slick set up for putting in on and off. the POI shift really was not to bad, it more than 1 MOA to be sure but i'm not long range marksmen so is not a big deal. on a 18" barrel its very quiet too, no need for ear plugs.