I agree with Paul. Selway bolt on is the most solid. Even though the GN bolts on, it's still only a wire, not a flat piece of steel or aluminum that holds the two quiver pieces. Thus, there is some movement there. Lots of folks don't mind that though.
Both are quiet. Selway is a bit larger. The hoods themselves can vary in size. I try to buy the smaller ones, and sometimes trim off 1/4-3/8 of an inch around the base of the hood. I also use a four arrow gripper. Pretty compact when I'm done. Certainly doesn't look too big on a three-piece bow.