Are you right or left handed? While making adjustments when mobile is not good practice it is still handy to have easy access while parked or waiting at lights. Nice for the family to watch maybe but the driver is the one that has to follow the map so placement should be best for him/her. Although voice can give you directions there is better situational awareness with a quick glance at the map, giving more notice when lane changes are needed for example.

Placement to avoid sun glare on the screen is also a consideration.
Mine is mounted on a suction cup on the windscreen to the right of the steering wheel (right hand drive, right handed driver). The other option, a bracket on an airvent, is too low. By coincidence this places the unit just above the vent which gives it ideal cooling when outside temperature is in the high 30s and the battery is charging.