depends on what kind of music u listen to for the sub size. Personally i believe 12" sub is better as it does not lag as much. As for choosing a amplifier the best value for money is the Jaycar brand RESPONSE. It not only has quality but a heap load of power as well. Make sure you do your research though cos u dont want to buy the wrong stuff. look for a 2ohm dual coil sub. i have researched subs imencly for a presentation at uni and have found these to be the best. Also make a custom box however look on the net for the formulas to ensure you get the volume size correct in proportion to the size,rms,vp-p ect.... Good luck mate
