The suggested placement of your child (assuming one) is in the middle rear passenger seat (the caveat being if correct install of the seat can be achieved there). For 2 or more children....the forward facing youngest child is safest in the middle rear. The rearfacing child (and other remaining occupants) should be placed in either of the rear outboard positions. Technically, if you are in a crash, the side of impact becomes the less safe side of the two...so it becomes 50/50 when trying to choose between the rear passenger side vs. the rear driver's side. It was once thought the passenger side outboard position was slightly safer than the driver's side rear outboard, however the percentage is slim. (1-2 %) Because the rearfacing child is better protected due to the postition they face, coupled with the design of the shell of the seat which "cocoons" them, that is why it is recommended to put them in an outboard position when securing more than 1 child.
There are four types of crashes. Frontal, Lateral, Rear-end, and Rollover.
The frontal crash is not necessarily the most severe, but is the most frequent type of crash. The lateral (or T-bone crash) crash is typically the most deadly. There is typically less space between the encroaching vehicle and the occupants of the struck vehicle, thus more severe injuries can occur. There are minor differences between fatalities between the right and left side of the vehicle...it just depends on where the impact takes place.
The rear-end crash accounts for just 3 1/2% of fatalities. Typically these types of crashes occur when both vehicles are moving forward, or when the front vehicle is stopped.
The roll over crash involves the vehicle rolling over onto its side or top, one time or many times. This type of crash is typically fatal as it often results in ejection from the vehicle. Ejected occupants are 4 times more likely to die.