I did them in Spain. Honestly German taxes were a bit more intimidating (so many fields, tk is different) but in the end you only need a few. As a salaried employee you can use taxfix and get it done in 20 min.
In Spain they were easier, but also I could not expense many things as a contractor. In Spain they would send you a draft, and you can request a meeting to help you do them (few people do this). This was smooth. You show at your timeslot and a friendly person is there for any questions. Before you leave, the definitive version is done.