There is no such thing as a full-band mobile antenna on VHF!

There is no such thing as a full-band mobile quarter-wave antenna on VHF. Anyone who is trying to sell you this idea is being dishonest (or doesn't know what they are talking about).

For example you may be told (or shown) VHF 136-174MHz. In reality, the antenna would need to be tuned for a particular center frequency within this band and will only cover approximately 5MHz above and below that frequency. For example, an antenna like this would need tuned on 160MHz and would give a VSWR of less than 1:2 between 155 and 165MHz.

There may be specialist antennas out there that do indeed cover the VHF entire band, but performance (i.e. gain, radiation pattern, VSWR curve etc.) is significantly compromised to achieve this.

5/8 wavelength antennas may have slightly better badwidth but this is being masked by the loading coil. Yes, 5/8 wavelength antennas have got more gain but I'm only considering the quarter wave.

The Discone antenna may cover a few hundred MHz but would not be practical for mobile applications so I've excluded this.

Having a VSWR of less than 2:1 (or as close as possible to 1:1 on all transmit frequencies) is important, as a high VSWR will have a negative impact on radio performance and reliability.

The specifications, for the majority of Motorola's quarter wave mobile antennas, state that they only cover specific portions of the VHF band, because that is the inherit properties of a quarter wave antenna, and because these antennas require no tuning.

UHF (and upwards) is a little easier: that is because the wavelength doesn't change that much across the band (0,1m versus 0,53m) so the physics of making broadband antennas at those frequencies are a little easier in this sense.