Wagner is the place to go. Or the Apfelwein place next to it, forgot the name. The Schweizerstr. area is better (less tourists) than the other area in Sachsenhausen where all the other restaurants are.. "Klaane Sachsehaeuser" and others.
Warning: The food is not very good, and Apfelwein is not everybody's taste.. Still, go there, you will have fun and it's not expensive at all.