The C van cab and more forward engine position offers greater driver/passenger protection in a front end collision and slightly better protection in a rollover.
The C's driver and passenger front doors are nice. Most A's only have the one house door.
C's are not available in rear diesel engine configuration. Rear engine configuration allows huge storage compartments underneath the coach body.
A's have more useful space per length than C's, since they don't give up the first 5 feet of length to the engine and cramped van cab.