I definitely haven't found anything better which is also relatively available in the US. But I think that Königsberg-style marzipan is way better than Lübeck-style (and would do so even if my mother weren't from East Prussia. :)
Really curious what the difference is. I've seen marzipan in old town Tallin, the capital of Estonia. There seems to be some baltic old Hanseatic League town connection here, as Lübeck where Niederegger comes from was also in the Hanse[0].