I've got the Britax Hi-Way. It fits really well into the Renault Scenic (07) - tons of space for lo's legs and, even though the front passenger seat is at its furthest position, there is still a good couple of inches between the back of the seat and the back of the car seat at its highest recline.
I did, however, first have this seat in a Honda Civic (06). Whilst the seat does fit into the back passenger seat I found it so difficult to get lo in and out. Due to the sloping of the rear door, I had to lift and twist lo to get him out and he's only 9.5months - I dread to think what it would be like for older babies. It was a painful experience both for me and lo, hence the change in car