If you're doing auto's on a veg lighting cycle then I would just stick with auto's, especially if you're looking for a decent yield.
You are capable of getting big yields from 12/12 from seed with photoperiod plants, but it takes a lot of practice. I'm doing 12/12 from seed simply because it's easier on my electricity bill, but I'm not expecting much from my first grows, maybe an ounce at best, who knows.