Magnetic or clamp car mount — which holds better?

A clamp grips the phone mechanically, so it is the safer choice on rough roads and with heavy phones. A magnetic mount is faster — you place the phone one-handed — but holding force depends on the magnets: MagSafe-standard mounts hold well, while a thin metal plate under a case holds noticeably less.

Does a magnetic mount work through a case?

Through a thin case (up to roughly 2 mm) a MagSafe mount works, though the hold weakens. A thicker or rugged case pushes the magnets too far apart — in that case choose a case with magnets built in, or an adhesive metal plate.

Where in the car is the best place to mount a phone?

A vent mount is the most convenient and does not block your view, but in winter the warm air blowing through heats the phone. Mounted on the windscreen or dashboard the phone sits more steadily and closer to your line of sight — just make sure the mount does not obstruct the road.