I've owned both an AT & MT 370Z.
It really depends on what you want to do. The MT has
you more involved in driving the car, and there is a lot
internal satisfaction and daily enjoyment derived from that.
When driving the AT in (M)anual mode you physically
feel a layer of abstraction (or separation) from the
car when driving. That said, I have seen a report that the AT has
put down faster 0-60 & 1/4 mile times due to the
*quicker* shifts (see article
here). From experience, I will
definitely say you will want to drive the AT in M mode all the time
(for performance reasons). Also, know that the paddle
shifters with the AT are quite nice and can be used at any time
(in Drive mode or M mode); you lose this option when having a MT.