I'm assuming that you are looking at 2 subs for a home theater setup. For a home theater setup, you would want to get a larger sub like a 15" or an 18" for more slam/boom in crashes and explosions. These larger cones tend to be more sloppy and slow. (the larger the surface area, the slower it is going to move and stop). If you are looking for a sub for a musical setup, the smaller the driver the better. (most decent speakers do not need a sub for music in the first place. If you have the right room, the right setup, and a decent 2/3/4 way speaker, you will get a more true-to-life sound than emphasizing the bottom end. For example, read reviews of the famous Revel M20 small monitors, the reviewers indicate that they are not missing anything and prefer the sound of the M20's without a sub). If you think you still need a sub, try to audition one that has multiple small drivers which will be faster and more accurate than that of a larger more sloopy driver setup.