I suppose it depends on how much you want to pay for a mount.
I use the Brodit mount for my smartphone.
They do specific holders for different phones and SatNavs, and I have had no problem with mine.
They are in two parts - a clip specific to the car, and a mount specific to the SatNav / Smartphone.
There are a few versions, depending on which vent you want it on, or one attached to the A-Pillar, or in the centre.
This is an exampe of just the mount on the A-Pillar
They are not cheap, but seem very well made and excellent quality