Even an overripe banana is better than most things people might reach for instead. Don't stress about banana ripeness - pass on the cookie and eat whatever banana you like.
Somewhere between ripe and overripe for me. If I eat them, which is rarely. I usually just buy them once per season, let them get too ripe, and make banana bread / freeze for smoothies.
Unless you are making banana bread, in which case overripe is best. My banana bread is top-notch. The secret is to sprinkle a generous amount of brown sugar on top before baking. It caramelizes and makes it into a heavenly treat.
I was just thinking about how weird it is that,as far as I can think of, bananas are the only food I still eat when it starts changing colors while sitting out on my counter.