Larsen Base Station Antenna - 5/8 Wave - Cable with BNC Connector Included
This is a very nice base station antenna for use on your truck or RV.  It includes metal clamping straps that can be used to attach it to a vertical rod or bar.  The antenna is tuned to have optimum performance at 123.3 and 123.5 MHz but works well over the entire aviation radio band of 118 to 136 MHz.  It includes an 5 m (16.4 foot) long cable with BNC connector for connection to your handheld aviation radio or base station radio.  The antenna is much longer than the 1/4 antenna and offers better performance.  However, its long length makes it quite flexible.  It is probably the best option when the vehicle it is attached to is standing still, but perhaps not when the vehicle is moving.  The 1/4 antenna is probably the best option for use on a vehicle in motion.

This antenna includes 4 radial antenna rods which act as the ground plane.  No additional ground plane is needed.

Length of antenna: 60.7 inches (154.1 cm)

The antenna length was optimized using an MFJ-259B from MFJ Enterprises, Incorporated.  It allowed me to quickly measure the antenna's VSWR across a range of frequencies and find the frequency that works the best at the given length.  Below are the test results.  Since this antenna mount includes 4 radials, a ground plane is not needed so testing was done without any ground plane.  

Summary of the Test Results
The test results show that the 1/4 wave antenna is not quite as good as the 5/8 wave antenna at the frequencies for which it was optimized (123.4 MHz), but it is close.  The 5/8 wave antenna has a slightly lower SWR at the frequency for which it was optimized (123.4 MHz).  However, the 5/8 wave antenna has a narrower frequency band than the 1/4 wave antenna.  It is still excellent at 122.8 MHz and not bad at 121.5 MHz, but it is not great at the extremes of the aviation radio band (118 and 136 MHz).  That is fine since most gliders operate in the 122.8 to 123.5 range.  The 1/4 wave antenna is not quite as good as the 5/8 wave antenna at 123.4 MHz, but it is still excellent with an SWR of 1.2.  The 1/4 wave antenna is still quite good at 121.5 MHz and not too bad at 118 and 136 MHz.  The 1/4 wave antenna is much better at 118 and 136 MHz than the 5/8 wave antenna, but I don't think I've ever used those frequencies.  One other consideration is that the 1/4 wave antenna is quite stiff so that it will remain nearly straight when on the roof of your car or RV at highway speeds.  The 5/8 wave antenna is much longer an much more flexible (bendy).  It will be bent back dramatically at highway speeds.  The bending will not damage the antenna and probably won't hurt its performance very much, but it is safe to say that the 5/8 wave antenna is better for stationary applications while the 1/4 wave antenna is (perhaps) better for use at highway speeds
.