If you go for the Piett Defection scenerio or not it would still be more visually interesting to have the Executor crash into the incomplete side of a/the Death Star.

Imagine that great blue arrow plunging into the exposed ribs of and girders.

We could see it falling down and down through the superstructure until it reached a surface to collide with with bits sheering off it on the way down creating there own explosions.

It would do a lot more damage too as the final explosion would be nearer to the core (possibly enough to take out a whole battlestation if you went with the 2 Death Star scenerio).