I went through this same dilemma a couple of years back.
It depends on if you value space or maneuverability more.
If you need your space, and think youll spend most of your time out in the wilderness for long periods, a fifth wheel will probably be best.
If you plan to travel from city to city, however, you'll probably find a fifth wheel impractical and a small class C to be far more maneuverable.
As far as truck campers, all I can say is I really wanted one until I realized they are the worst idea ever. Aside from the obvious fuel inefficiency, they'll cost you more over time in repairs because regular truck frames and chassis are not durable enough to haul the weight of an entire other vehicle around all the time. They also have much smaller holding tanks and generally (though not always) are designed to lower standards than a vehicle/trailer and are more prone to leaks and wear over time. And they're really difficult to mount/dismount from your truck, so you'll essentially be driving an extra-heavy camper with bad fuel efficiency where you don't even have access to the living compartment. The ONLY reason I'd ever recommend a truck camper, is if you already have a truck that you don't wanna part with.
I have a small, 17 foot class C camper, is pretty ideal for inner-city camping (I can park in friends driveways or any on-street parking spot in any city) and light/short-term wilderness camping. I also really like that it is one vehicle (as opposed to a truck or trailer camper which are separate compartments) because it allows me to hang out with friends/hitchhikers/whatever when I'm on the road. Like, last week I travelled to Louisiana with some friends in my rig, and we made breakfast while on the road and ate together in transit and frequently traded off driving shifts (the 5 of us couldnt do either of those in a trailer/truck camper), and when we got into Baton Rouge (a city where we knew no one), we didn't have to worry about our rig being too heavy/bulky to maneuver around city streets or about where we could leave our trailer/trunk camper parked in the city without it getting towed/stolen, while we took our truck around exploring... our home IS our truck.