Think of it this way. an 8 arm has 3 slits each, which equal to a total of 24 slits. (the open end of the trees is for reducing drag, and in theory gas has to be existing all the slits above it before gas can exist the holes) a circ is generally 20-24. The diffusion isn't going to vary enough between the two too truely have an impact on your decision. They are both going to hit just fine. I would make the decision based on personal preference. If you already own something with a tree or a circ, get the opposite. I just like circ's better because it takes less glass and you get the same amount of diffusion points. And if your a sucker for stacking bubblers, a circ is better for that.