If you have the money, I would go to the larger cage, extra room will be a benefit a male or female. Down the road you may get a bigger cham, and wish you had gone bigger.
I have a male veilded cham but hes still young. I have a 24x24x36 enclosure now that i made but i really like those dragon strand enclosures so ill take your advice and go with the 2'x2'x4' when he gets bigger thanks