For our "big trips" we have a bed set up in the vehicle, and this is our preference, however we have experience with RTT and ground tents:
1) Roof top tent - we used this in a rental vehicle for 5 weeks. It made no financial sense to ship our own vehicle for a 5 week trip, we needed a 4x4 (for access to the high country), and didn't want to/couldn't afford to pay for a huge 4x4 camper. We had seen others wrestle with RTTs, taking anything up to 45 minutes or so to put up/take down however thought it would be good to have some experience.
So - a rental vehicle with a Columbus Autohome RTT. It worked very well - 2 minutes to put up/take down, comfortable, warm, good shelter. No complaints, and we solved the question of having to climb down in the middle of the night. DIsadvantages: more wind noise, more aerodynamic drag, hence slightly higher fuel consumption, higher CoG with impact on stability, although this RTT is very light so didn't have that much impact. Overall it was a very good solution to our needs for this trip.
2) Ground tent(s) - we have camped in ground tents over many years, however had not done so for a long time. This (northern hemisphere) summer we needed to travel as a group of three, so the bed in our vehicle was not going to work. The solution was to buy two ground tents. This worked very well for this 5 week trip. Time to set up was around 20-25 minutes (2 tents). Some sites had very stony ground and putting in tent pegs was occasionally challenging. Some sites were not as flat as one would hope so there was some juggling of location to get it right. Putting away two wet tents after a rainy night was slower and inconvenient in terms of keeping other stuff dry. The tents took up some interior space, however not that much, and the mass was kept relatively low.
So - horses for courses! We continue with the approach of using a bed in the vehicle as the best for us on our "normal" big trips, however both the RTT and ground tents have worked for us when circumstances required a different approach.