I don't know the biomechanical difference. I just like reverse more because forward lunges seem to hit my quads more whereas doing them reverse I am able to concentrate more on hitting my PC. If i do them with my front foot elevated I can feel the difference in hips - because it becomes sort of like a one legged squat (if you do it correctly where you are basically using your other leg - the leg that is moving behind, as a source of support only).
I prefer reverse lunges and walking lunges. I don't like forward lunges at all.