A few questions about RTT.
1. do they all have a rain fly? is it permanently installed?
it looks like royal pain to put on with tent height.
2. I need one for family of four. which one has 4 sided annex
and floor?
3. which one has most comfy mattress?
Not all have flys, Autohome Overcamp and Overland are a couple of example without. For the ones that do have them, they self deploy so height isn't a factor. As Bunduguy noted, there are different designs out there.
A Mombasa and similar Covered Entry models have a four sided with floor Annex. Two in the tent, two on the floor depending on size. I'm not familiar enough with all the high-end model to know which have four walls with floor annexes.
Mattress is subjective and weight dependent. I'm about 165, I find a Mombasa mattress just about right but a AutoHome Overcamp to hard.