I could ditto a lot of the comments on why we chose C over A, but one thing that hasn't been mentioned is height.  Our C is 31 feet, so it is pretty big as far as C's go, but we still hit a lot of state parks and such.  But, even if access is decent for a longer rig, the branch overhang is often bad enough with a C but it would be impossible with an A.
The other thing for us is the time factor.  We figure that a Ford Econoline chassis can be looked at and fixed in darn near any small town across the US rather than having to be towed somewhere for work.  Not a big deal with roadside and towing coverage, but a big deal to our time budget since we're both still working full time and we have a school aged kid.  When time isn't so much the essence this won't weigh in as much for us.
I think it really comes down to your plans and your camping crew and your style.