I'll give it a shot
it all depends on what your plans are and space available..
if you are limites in space and want a big collection of ball pythons, then going with a rack system would be a better option..
if you are thinking of getting just a couple of your favorite morphs, then getting a nice 48x24x28H cage ste up with a natural setting would be more rewarding for your pleasure of viewing them..
setting up a pvc cage, would need a UTH source and a radiant heat panel on the top side to get nice ambiant temperatures.
this cage size gives you lots of room for decore, nice size water bowl and room for the snake to explore.
rack sysytem has smaller available space for the snakes, but ball pythons do well in these systems, specialy if you plan on breeding in the future.. you can have 18-24 ball pythons in a rack that takes the same space 4 pvc cages and 4 snakes would..
in the end, it's more about what you desire,,
-natural big cages for the snakes to enjoy
or
-rack system to keep more of them in less space