Batboard

I was curious as to what you guys thought was better as far as TX / RX range would be considered. I'd assume the 5/8th wave would have better performance than a 1/4 wave, no ? This is for a UHF A7 Spectra, and the antenna itself is mounted on a trunk of a 2011 Crown Victoria. Most of the time the radio is used in fringe areas, on Simplex.

What type of service area are you running in 99% of the time?
This will indicate the best antenna for the best coverage you need.
Urban areas with tall buildings usually have better results with 1/4 wave antennas, as the signals get up and out better. With flat terrain, such as large, open fields and such, a gain antenna would probably be a better choice, especially if your day to day usage will be at a farther distance than you would be in an urban environment.

Get two, use the one that works best for your day to day comms, but have a spare to swap to in case you get caught having to go where you normally never go.

The gain will only be in the 3-5db range. Whether that makes the difference for you depends on the receiver at the other end.