I'm not sure one is vastly better or easier overall for handling, though there are differences to be sure. For that matter, a diesel pusher with air suspension handles rather differently than a front-engine gas motorhome with leaf spring suspension, even when both are class A motorhomes.
The class C's on van chassis tend to be less maneuverable than similarly sized class A motorhomes because the van chassis has a rather anemic wheel cut angle. Some people find the van-style cab with at least a stubby hood a little less intimidating to drive than a typical class A, but I think that's more a matter of perception than anything. It does take a little getting used to steering when you're over or in front of the front wheels.
For what you're considering, I agree with the others that handling ought to be rather low on your list of priorities. Obviously you do want something that you can safely drive from place to place. (If these work sites aren't too far removed from each other, it might even end up making sense to drive the car separately rather than getting it set up for towing. That would certainly make maneuvering the motorhome in gas stations and similar places a little less stressful.)
Also note that overall length has relatively little bearing on handling on the highway; the width and height of the vehicle are more concerning than its length. Don't choose something that's too small for you just because you think it will be easier to drive.
