When you're eating a banana, straight from the peel, it's a matter of personal preference. My husband likes to eat them green, and I like them speckled but still firm. However, baking with bananas is a different matter. Overripe bananas are easier to mash and will mix into your batter more smoothly. Overripe bananas are also much sweeter, which makes a difference in the taste of your baked goods.