I also have both, and while they're both good, I think the great northern is a little better. The problem I run into with the boa is that hood portion of the quiver tends to rotate after a few shots, which loosens the hold on the head of the arrows. The great northern has a rod system that connects the hood to the arrow gripper and prevents this problem.
On the great northern the foam is recessed a bit from the edge of the hood, so it's easier to get broadheads covered. I also find the fletching clearance to be better with the great northern.
Again, they're both good, but if I had to pick one, I'd pick the great northern.