I’ve not owned an NX, but drove one for a few days. I much prefer the RX. As has been mentioned, get an insurance quote before you plan as it seems all Lexus models are attracting high premiums recently
I’m 6”3 and have found my preferred/comfortable driving position in my RX without the driver seat fully back. There is therefore plenty of room in the back behind my for an adult to be comfortable too. Our family has two children and a dog and on a recent 1000 mile trip with everyone’s luggage for 4 days away, the boot was big enough for my wife to find space to bring things home. It’s not best in class for space, but it’s more than big enough in reality.
All around, it’s a difficult car to fault. Comfortable at speed, takes imperfections in the road well and, for a 3.5 V6 SUV, is economical at around 35mpg.