iPhone. Duct tape it to the outside of a tire,
Just kidding, I'm an Android fan.
I have a RAM X-Grip mount and a RAM universal finger grip. The X-Grip is handy. But with the medium length fingers, and the bottom stop arm in place, the Finger Grip mount is much more secure IMHO. I now use the X-Grip only in the car.
I also stuck one of the non-slip mats to the back of the finger grip mount to make it even more secure and to add a bit of cushion. I've actually been using this setup for a number of years. The only issue I've had is rain.
I have an Aquabox for rainy days. The Aquabox sucks. It is very difficult to operate the controls. The extra layer of rubber cover make so much glare that it is hard to see my maps. And if you are charging the device inside the case, in the sunlight, it can over heat. It is basically an oven.