This probably best belongs in the Zombicide game page forums but overall my favorite additions have been small ones like the Zombie Dogs and Angry Neighbors. Once you've done all the base game missions then the big boxes like Toxic City Mall and Prison Outbreak will be more useful.
Ah it probably would have been better to post it there actually! (Sorry we are still new here and learning the ropes!)
Is there a reason that the smaller ones stood out more for you? We still have a lot of play to get through the base set but we are planning ahead because we can see this being a regular one for us.