Antenna is far more important than output power. Far more. Are you talking handheld or vehicle use? Probably the easiest is to get a GMRS license and use a good antenna. You can also setup a repeater if you have the know how. If you are or are willing to get a ham (easy) you may have a number of repeaters already in your area that would make it simple.
Agreed.
Handhelds are line of sight. A good antenna will help some, but it can't magically solve terrain issues.
Terrain is everything. There's a reason antennas are atop hills and buildings. A well placed repeater can do wonders, but you'll still need to solve power issues too.
Surprising though, text messages can often be more reliable than voice. Something to consider.
Good luck.
