Depends on your tastes and preferences. What do you like (cities, views, museums, old towns, countryside, mountains)? How are you travelling (car, train)?
You probably have some "Sprösslinge" (offspring) with you as you have included Europa Park. So that is probably un-cancel-able.
I would cancel Baden-Baden, little to see there.
Luzern is an outlier, but if you want a fix of mountains, you need to go to the Alps.
But, there is plenty more to see in Alsace (Colmar, wine villages), and on the other side of the Rhine (Freiburg-im-Breisgau, Black Forest).
You need to prioritise according to your preferences, and stay at least 2 nights, probably 3 in each place. 18/3 = maximum 6 places.