I know there will be lots of disagreement but here is what I do.
I have a mag mount antenna inside the trunk of the car .
The antenna is upside down.
The antenna is stuck to the trunk lid or speaker inside the trunk.
I run the cable inside thru the trunk and along the floor board, cable comes up next to the drivers seat.
Handheld scanner is kept in storage compartment.
Comet B-10 and B-10NMO. Comet B10 antenna
Comet Mobile Antenna Mounts
I use a comet B-10 with the cm5m mount.
You will also need a SO-239 (UHF) to BNC male adapter if your scanner has a BNC connection.
The 16 feet of cable let you do a nice installition.
This is done on a 2013 Nissan Altima
The antenna is invisible and works fine for my needs.