Is Class A smoother ride then Class C and MPG

First thing you need to do is to check your tire pressures. Often times tire places/dealers simply air up the tires to the max listed on the sidewall; that is WRONG and will result in bad handling, harsh ride, and uneven tire wear. The tire placard inside the RV near the driver's door will list the recommended tire pressures based on the maximum weight (GVWR, GAWRs) that the RV should ever weigh. You should never need to run higher than that (because you should never be heavier than that), and the pressures listed there will work for now. But the best way is to get your rig weighed (front & rear, or better yet, 4-corner) and set the tire pressures according the the tire manufacturer's load table. That will provide the best ride, the best handling, the best tire wear, the best economy, etc.