First determine if you have isolation problems, if not buy what looks good and fits the equipment. There are three sources of vibrations: the component themselves (mostly turntable/CD/HD related), airborne, and via the floor.
If it's component related (which normally presents as a smearing of the sound), try adding mass or clamping it down.
Turn the volume down! If the floors are "solid" your any differences in racks are solved. If you're a headbanger get a cabinet not a rack or move the equipment into a closet or another room.
More mass is always good. As mass goes up the resonant frequency goes down so the energy level needed to excite goes way up. Ideally the mass of your components would couple together and with the mass of the rack.
Isolation to the floor is good if the floor is "soft" (otherwise undesirable as the mass of the components/rack wouldn't be as well coupled to the floor).
Stiffening rack/cabinet components raises the resonant frequency but also the energy needed to excite.