Newbie Advice, SOG or SCrOG?

This is my first post here and my first grow. I built a 42" x 30" x 72" cabinet w/ a 600 watt switchable HID system. I currently have 21 seedlings that are just over a day out of soil. I am wondering if someone with some experience might help me decide whether SOG or SCrOG would work better and how many mature plants I should keep for the best yield. These are all bag seed seedlings growing in a fast draining soil/perlite mix.

Thanks in advance.