Nothing wrong with going either way but I can tell you that even as an avid autocrosser, I went with the 7AT and I'm loving it.
Nothing but a highly accurate timing system will discern any performance gap between the two and with Nissan's manual mode, you really have the best of both worlds.
If you really love to shift manually then get the manual but you won't be giving up anything with the auto (except a tired left leg/right arm when you are in stop and go traffic for a while
)