I use RAM mounts for mounting gps, iphone, ipad, etc. in my cars.
Here are some pictures of the setup in my car. It's a ball mount that attaches on the tube under the dash in the footwell, and an arm with any holder you wish at the end of it. Iphone holder in the pictures.
Advantages are no interference between passenger foot/knee and holder, no interference with gear shift. Can be placed beneath dash, just outside, or in front of dash with additional arm and ball joint, as well as into the sitting area if you want the holder closer to you or your passenger. Infinitely adjustable due to the ball-joint system, no "click stops" yet firm and tight grip due to slight rubber coating on ball joints to stop any motion or "creep".
I use one of the thicker arms to take the weight of my ipad with holder, to use for the TomTom app on a nice big screen.