the frosting. Period.
That is the one single part of a cake that can make or break it. The cake can be moist and delicious, etc, but if the frosting tastes like a cardboard box you might as well throw the cake away. On the other hand, if the cake itself is a little dry or subpar, homemade frosting that is superbly prepared can more than overcome the shortcoming of the cake itself.
Information you all needed. You're welcome.