Like Raul said you really can't overly gereralize for all snake species, you have to take each one on their own needs. However, a few generalizations I've found to be mostly true is that Larger species, arboreal species or active species do better in cages whereas smaller more secretive and less active species do better in rack systems. I keep most of my snakes in racks with the exceptions of my carpet pythons and burmese pythons which I keep in cages. One caveat I would like to add for ball pythons, I prefer a longer tub like the sterlite model 1960 or the Iris model CB-70. Not necessarily for the size, but because you have a much wider temperature gradient with the longer tubs.