What the two gentleman say are correct in terms of sounds from the two choices. Personally I find it that if you have a 10" once you hear a 12" you will want those. It has a lot to do with the amount of surface area the sub has (i.e. that is why a lot of people prefer KICKER SOLOBARICS). However it does depend on quality or the sub and amp, as well as location and enclosure. Hope this helps.
HU: Kenwood CD w/ Kenwood Chg
FRONTS: Kenwood DB+ Excelon 2-way 6.5"
REAR: Kenwood 3-way
MID/HI AMP: 400x4 Fosgate Punch
SUB: 12' Kicker VR
SUB AMP: 250x2 Fosgate Punch
**Soon to come... anything but those front Kenwoods, possibly Infinity Perfect Seperates