If it's a choice between a gutter mount or the middle of the roof, it's almost a no-brainer, take the center of the roof. AS far as the devaluing of a vehicle because of antenna mounts, go to another dealer immediately! As was already said, that's B.S. On a trade, they are already not giving you what the thing is worth, and repairing stuff like small holes is a throw away, they'll fix the dents/dings and other stuff too. It's a 'given'.
Greying old veteran of fire, police and emergency medical services here (read professional appliance operator) I breathe air today because twice, I had a good dispatcher and reliable commo. When possible, our antennas were center roof.
