To resume my experience - I had a normal ground tent, a good quality hardshell RTT - Autohome Columbus XL and swags.
Self inflatable mattress - they are a bloody curse . They sounds nice, you throw them out in the tent, wait for like 30 min, puff in them a few times and done ...right ? What nobody is telling you is the deflation process, that takes a lot of time and effort. From this point of view a normal pad or a normal inflatable one is much better/faster.
RTT. - canvas RTT the only added value is that you are off the ground. The setup very often is even more painful and time consuming that the most basic ground tents. Heavy compared with with ground tent that offers the same space.
The off the ground-safety factor.
I think it is more of a psychological effect. . I don't know of anyone dying even in Africa from sleeping on the ground. I think like 15 years ago there was a case of a german lady who slept with her feet outside the ground tent and a lion took a bite out of it, but that was about it. For some reason even for huge animals a bit of canvas with zipper seems like an impenetrable barrier ( i know it does not make any sense, a bit of canvas should be nothing for a bear or a lion or whatever, but is true) .. so there is no real value added to the safety factor by going on the roof. As long as you close the zippers you are good, in any tent, at least from large animals.
But if this is what it takes to get the missus out and the family to enjoy the trip ..it will worth any expense. and all other talk about weight up top, poor fuel economy cost etc becomes irrelevant :)
A hard shell it is a different ball game. They are in general smaller than canvas RTT, but the experience is different. Less impact on the aerodynamics and for most, the set up and fold is under 1 min. Heavier than cavas. Difficult if you have to take them off the vehicle often, you need some kind of pulley system or 3 buddies . Some canvas RTT - have the same issue, you need more than 2 people to put them on or off the vehicle.
Best RTT when money is no object that takes care of almost all disadvantages of RTT are roof top conversions. They are costly, but probably worth it it if you plan a 3 year trip around the world. For pickups there are options now that will fit almost any pick up, for wagons'SUV, there are some specific models, like defenders, troopies, jeeps wrangler, who have specialized companies on doing this type of work, so there the selection is more limited.
Swags - heavier than ground tents. Can be kept inside or on a roof rack, they can take some weather. They pack and setup fast, there are even some inflatable option with no poles. You can leave the bedding inside like it is possible in the good RTT's . This saves a lot of time and space . They come with a normal mattress that can be upgraded. But they are bulky and heavy. Where storage space is an issue.. they might be a problem. Cost is also a factor, they are for sure up there with the more expensive ground tents. but much cheaper than an RTT