I work in a city radio shop. We have hundreds of vehicles with various radio services - GPS, Wifi, cellular, and of course the two way radios. I can absolutely assure you that getting the antenna outside the steel box known as your car will SUBSTANTIALLY improve radio performance. Best bet is an antenna that is mounted on the roof with a hole drilled through the roof for mounting and routing the cable or cables. Likely the next best is a mag-mount on the roof - be careful not to damage the cable getting it outside. Through glass antennas are less effective than an antenna connected directly with coax cable. Any of these will beat an antenna inside the car however.