Indent! Indent!
To prevent or at least minimize banana breads or any sweet loaf bread from cracking in the middle, make an indent across the middle of the batter before baking.
This is how:
Pour the batter evenly into the pan. Then use your spatula to make an indent across the middle so that the sides become higher than the middle. This prevents cracking on top.
I have been using this hint for years and it really works!