In my short (2yrs) I have come to the following opinions:
Class C generally have lower roof height than Class A.
Class A generally have more generous floor plan size due to longer length and are a bit more comfortable.
Class C are somewhat easier to maneuver due to shorter length and lower height.
My 24 foot Class C gets 15 MPG on diesel, yours may vary.
Class A most certainly have more than one slide, sometimes three and have lotsa floor space when parked.
Class A will probably have a much bigger towing capacity than Class C.
More Class A than Class C that I have observed have a auto-deployable satellite antenna.
Thare are Class A that cost close to 1 Million USD. No Class C that I ever saw even comes close to that. I surmise that you are not looking for the upper cost level.
I believe that Class A gassers are generally less available than Class A diesel which are mostly pushers (DP).
Class C come with many chassis sources including Ford, Chevrolet, Mercedes Benz/Dodge (see Sprinter), and probably others.
Personal experience: Noise is not objectionable even with a front engine, it has good pulling power up hills even when towing. M-B does require use of certain approved oils and such.
Since I suspect your are rather new at this since you asked about this, I urge you to look at floor plans of prospective units as this will give you the best experiences IMHO.
Just added this: Class A definitely have more storage apace in the basement than Class C.
Happy trails and the best of luck to you in finding your rig. I hope it is as close to perfect for you.