The most critical thing for safety reasons is a holder that mounts the phone solidly in the best possible location where it can get a glance with a minimum of effort, is solid and unmoving, and is as close to normal driving line of sight as is possible without blocking the view. All other considerations are secondary. I mount mine at about the ten o'clock position in relation to the steering wheel, at the top of the dash, right next to where my right hand is on the wheel (I'm right handed). I position it so that I can glance at it quickly and easily without looking away from the road more than a tiny bit. The other safety thing is a mount that won't come loose and bury itself in your face in an accident.
Where I live, they can ticket you for any other mounting position, such as on the center console, etc., or anywhere else away from normal line of sight, because they know you will be unnecessarily distracted by that location. And they should, because if you do that you are a menace. The idea is to use your brain for something besides a donor organ, while you still can. Those with large OEM display phone control head units and steering wheel controls are the exception. I will be doing an upgrade to that in the Spring, but I will still put the phone where I can see it without looking down, because I will invariably look at it. I know, I've seen me do it.
