At the risk of heresy, I say when over-ripe is called for it is by the mistaken impression that the flavor is improved when it is only that it is sweeter, less starchy. Muffins will brown faster.
I believe this myth grew out of the fact that recipes were created to use up what would otherwise go to waste: it then was inferred that over-ripe is ideal.
My personal opinion (highly heretical) is that slightly under-ripe bananas yield muffins with more banana-y flavor (not burnt sugar flavor). I began experimenting after finding that banana chips are made from half-green bananas. A bit of acid in the muffin batter (sm squeeze of lemon perhaps) further brings out the banana flavor.
Starchier under-ripe bananas bake up fluffier relative to the brown ones -I don't even need eggs or egg sub!
In the end, it's all about personal preference but for recognizable banana flavor, bake up a batch each and invite friends to a taste test which has 'more bananas' in the recipe. I'm betting greenies.