I like to clear the highest obstacle by at least 2000 ft.
On short XC (2 hours) I will stay about 2000 ft over the highest obstacle, on
long XC (4-6 hours) I will get high, 12,000 or higher, depending on winds
aloft.

John Harlow wrote:

I'd like to get input on opinions on the "best" VFR altitude for a route.

It seems to me it's largely based on distance, winds aloft and comfort
level. Do you have a "rule of thumb" trading off altitude (and therefore
safety margin) to avoid headwinds? Or, if winds aloft are to your
advantage, how high would someone go in a 172 class aircraft before returns
diminish?