Rear access is ALWAYS better. If you have your components on wheels, then you must constantly move a heavy piece of furniture and have the opportunity to mess something up anytime it is moved. Plus, without rear access, you have to squish all the cables behind the rack against the wall - in ways you really can't control.
Blech!
Rear access allows you to bring all the cables into a very structured cabinetry area and have full access to every single piece of equipment. Cabling can be fully controlled and hookups can remain solid throughout the seutp. Instead of fighting with cabling, every wire is put in its place and doesn't have to be disturbed every time you need to work on the equipment. It is far less of a headache, and much easier and more reliable for service and installation.