The folks at Winner sent me the Montar universal car mount to try out. I was already happy with my air vent mount, but I was willing to see how it compared. As soon as I started using it, I realized I would never go back. This thing sticks to my windshield and simply won't budge, no matter how much torque I apply while inserting/removing my phone with one hand.
The suction cup is coated with a very sticky rubber. It reminds me of those toy octopuses that stick to the wall when you throw them. It adheres well to the textured surface of my standing desk. It does not stick to the dashboard of my Prius, but it comes with a plastic disk that you can stick on the dashboard, which will stick to the suction cup. (I'm not going to use the disk because I am concerned it will mar the dashboard.)
The rubberized spring loaded jaws grip the phone so firmly that there's no chance it'll pop out should you drive over a speed bump or pothole. The jaws open wide enough to hold my iPhone 6 Plus in its case.
Check out the video below for a demonstration of this excellent car mount.
Montar Universal Car Mount ($(removed)) on Amazon