If you search the forums (not just this one, but Escapees and RV-Dreams, too), you'll find many discussions on this. You also don't say what type of Class A you would consider... a $750K diesel pusher with a tag axle or a 30' gasser. There are many differences there. Fifth wheels also range from light-weight (well under $75K) units to 20,000 lb. almost-$200K units. If a fifth wheel, you'll need to consider a truck that will not only pull it, but handle the loaded pin weight (payload for pin weight is nearly always the limiting factor - especially on 3/4-ton and single-rear-wheel trucks).
Here are some of the reasons we are full-timing in a fifth wheel:
1) We already had a tow vehicle (diesel truck capable of hauling the RV we wanted).
2) If something were to happen to the drive-train of our "home," only the truck goes in the shop and we still have our home.
3) We have had conversations with people who have full-timed in both fifth wheels and class A coaches (larger diesel pushers). Every one of them said they had more living space and a lot more storage space in the fifth wheels. Our fifth wheel is very comfortable for us.
4) To be fair to the "other side," I will say that being able to pull over on a stormy night, turn off the engine, and push a button on the auto-levelers would be very nice.
5) We chose to keep our Toyota and my wife follows behind on travel days. Another plus for the Class A would be to be able to tow the car and have my wife ride with me in the RV. On the other hand, she says that having that time to herself listening to her music or books on CD is "the secret to the success of our marriage." We spend less than 5% of our total time on the road, though, and like to keep travel days to 200 miles or less. It's really nice to have the car - whether your in an A or a fiver - for shopping, sightseeing, getting into larger cities, etc.
Rob