I wanted to throw out of post of good commercial antenna's that work great for GMRS as well as other LMR applications. Every antenna listed I have used for home and on towers and have had little if any issues with.
Laird - Laird FG Series is a great antenna for home use and limited tower site use. Great for a home repeater when a tower is not available. Mostly omni.
FG4500 - Unity Gain Fiberglass Antenna N Female 100W 450-470mhz - Cost around $125
FG4603 - 3db Gain Fiberglass Anten