An article in the Times (Driver Health: Danger, incorrect use of your car can damage your health) quotes a study in which car seats were assessed according to health aspects. After that, the Volvo V70 wins before the Mercedes S-Class. How many types have been tested and how serious the study is, is not taken from the article. It is also recommended that car seats are not set completely vertically, but have a slope of 10% (against the vertical, not the horizontal ;-). It is not specified which model year of the V70 has been taken into account.