ermm.. be clear bro.. r u tryin to know the diff or u want to know the best sub..!! newayz to answer ur Q..
a DVC stands for dual voice coil n the other one which is 306c is a single voice coil sub.. dual and single voice coils subs are two very diff types .. it helps u wiring a sub to ur amp correctly depending on the stability of ur amp..
lets suppose if ur woofer is a 4ohm DVC sub n ur amp is 2 ohm stable amp then u can connect ur woofer wiring it in parallel to make it a 2 ohm load as ur amp is also a 2 ohm stable amp so that ur sub can get all the power ur amp can provide without ne danger of blowing ur stuff up
.. This is the only correct way to wire ur subs with ur amp