[Nexus 5X Accessories] Pandages:
As a car guy, I always struggle when attempting to tackle this problem. Here's 3 reasons:

1) Cars with stiff suspensions subject the passenger compartment, including the dashboard, considerably harder than soccer-mom-friendly economy sedans.

2) Cars with deep or substantially curved windshields can make suction-cup mounts a difficult problem.

3) Aftermarket tinting can be damaged by certain types of mounts (namely due to the stabilizing compounds in the rubber or silicone used in suction cups).

And here are my placement rules:

1) X-Y Placement. If possible, the phone/nav should be placed on the driver's side, between the steering wheel and the driver's side door. In other words, it should effectively hover in front of the A-pillar. In this position, it provides the least interruption to the driver's view of the outside world, and is particularly easy to reach when input is required.

2) Z Placement (depth). The phone's Z-axis placement should be roughly the same as the instrument cluster. In other words, the same distance from the driver's eye as the speedometer or fuel gauge. If this isn't possible, then it should be closer to the driver, not further, because unlike the instruments, the phone may require input (do not touch your phone while driving. Pull over, or at least wait for a stoplight).

3) Good Cable Management. Ensure that any cables run between the phone and the vehicle (e.g. a power cable or headphone cable) are well-controlled so they do not interfere with the multifunction switches or arms around the steering column. Use velcro or zipties to manage your cabling. Consider your vehicle installation permanent, but rapidly removable, so prepare your cables and mounts per vehicle and avoid removing them.

Shows correct X-Y placement, and good cable management, but sub-optimal Z placement (too close to the driver).

[IMG="Mostly-Correct Placement"]http://www.subaruoutback.org/forums/attachments/gen-4-2010-2014/27269d1360041711-looking-alternative-mounting-locations-garmin-gps-garmin-post.jpg[/IMG]

NOTE: In the USA, several states have made mounting anything to your windshield illegal. Several other states have restricted placement, and the guidelines I have posted above comply with most of those restrictions (specifically, California and Maryland, this placement is the only legal option). There are some other states that require passenger-side placement but that makes the units practically impossible to view for the driver, so they are effectively banned.

So far, I've had a few successes, and a few major failures. Specifically, failures with magnetic-type phone mounts attached to ball-joint arms, attached to the windshield via suction cup. These style mounts seem to work well, right up until you hit a significant bump. Then, either the magnet gives way, the ball-joint wiggles loose, or the suction cup pops free. In all cases, you can wind up with a phone near your pedals, and that's a huge risk.

I had great success with the Galaxy Nexus car mount (the cheap Verizon version, not the awesome google+samsung version from Europe) several years ago. When I upgraded to my Nexus 5, I was unable to find a sufficient solution, despite many attempts. I tried using the Nexus Wireless Charger as a mount, but the magnets in it were insufficient during bumps.