Argh, I typed a lengthy reply in another thread but it was closed before I finished and I lost the whole thing.
I drive for a living and record video. I have had two mounts for my iPhone 4, one from Boxwave and the Kensington K39256US Quick Release Car Mount. Both attach to the windshield with suction cups connected to a flexible gooseneck arm.
The Boxwave broke after repeatedly trying to wrest it into position. It comes with a fitted case that can be detached from the arm, and I did not know if it would fit the new phone, so I ordered the Kensington, which uses a clamp that should fit most smart phones, even in a case. I found it easier to snap the phone in and out of the clamp than with the Boxwave. Also, the gooseneck arm is longer and more flexible, and it is a lot easier to position for shooting video, and therefore less likely to break. The clamp itself can also be detached from the arm, and can also be attached to another clamp that fits in dash vents. The clamp can be easily ratcheted 90°, so you can switch from landscape to portrait. The Boxwave has a nut that you have to reach around to loosen and tighten every time you adjust it.
I cannot say that it's "the best", but between the two I tried, the Kensington was definitely better than the Boxwave.
It looks as though the new phone might fit the Boxwave case after all; I'll find out on Friday.