It's all about what you're going to be powering them with. The biggest advantage to having a DVC (Dual Voice Coil) subwoofer is that you have additional wiring options. So if you have an amplifier that makes full power at 1-ohm, you would want a DVC subwoofer that had dual 2-ohm coils. Or you would want two DVC subwoofers that had dual 4-ohm coils. With either of these configurations you would wire the subwoofers in parallel from the amplifier to produce a 1-ohm nominal load on the amplifier. If your amplifier produces full power at 2-ohms you would want a DVC subwoofer that had dual 4-ohm coils.
So a subwoofer that had dual 4-ohm coils could have the coils wired in parallel, producing a 2-ohm load, or wired in series, producing an 8-ohm load.
There are other properties that the subwoofer gains as far as T/S (Theile/Small) parameters go, but generally, from what I've seen, they are negligible.