the a14 hasthe best comprimise of bore and stroke. It has more power than the a12 and can rev harder than an a15, due to lower piston speed. If your not going to rev the ring off your car then the a15 will deliver good torque. It has to come down to what type ofuse the car will see. Also unless your 1200 head is a "gx " one , ditch it and go for the 1400 one .(Bigger valves bigger ports) My preference would be for the a14.
thats my two cents.