Are you talking mobile to mobile or mobile to repeater? Mobile to mobile is going to vary greatly depending on elevation between the two radios. I can use my handheld to talk 35 miles to a repeater but can't get 3 miles to my mobile due to landscape.
My 50W mobile with the MXTA25 Ghost antenna could go 20 miles to repeaters when I was travelling thru flat IN, IL, WI country. I switched to a Laird BB4505CNS and got another 10 miles further thru the same area.
Repeaters "generally" have antennas much higher in the air thus the greater distance.
I have mounted both mobile antennas on the side of my Jeep hood as well.