Pleas excuse a newbie still trying to understand things...

I realize, some of you value fares because they are First class or biz class etc. However, for arguments sake, lets say I don't value extra comfort and am only thinking how to get most miles per dollar. So, questions for the experienced members here:

At what cost per mile, do you consider a trip to be a good mr?

At what cost/mile would it be a great, memorable mr?