My wife and I will soon be in the same situation but have already agreed on our choice. For us, it basically came down to our travel style.
Truck Camper - good for exploring and not staying long in one place. We never unload so we always have everything with us.
Fifth wheel - great for staying in one spot for a week or more than moving to the next base.
Since we know the first few trips will be quick exploratory, we will be sticking to the truck camper. But when we decide to slow down, we have two thoughts. Either a motorhome with a small truck camper in tow or a small truck camper with a good size TT. Either one we will have the room yet still be able to explore the back country with comfort.