I'm sure that either one is capable of rattling your trunk off it's hinges. The question is, which will be the cleanest sounding. If space is not a concern, I'd go with the largest sub so long as the amp you're using has the necessary RMS power to correctly supply it.
If your amp is on the cusp, then I'd go with the smaller power requirement. If it's a powered sub then you're back to available space being the only consideration.