Hi uvsb, It depends on whether you would like to speak "German" German or "Austrian" German. In Austria we use the informal "Servus (mach es gut)", "Baba" oder "Griaß di" and the formal "Auf Wiedersehen". Unfortunately, however, "Tschüss" is increasinglingly replacing the good old Austrian forms in Austria, too. Kind regards, Georg

"Auf Wiedersehen" is very formal and "tschüss" is informal, but more and more the infromal "tschüss" is used in Germany. With your family and friends you would never use "auf Wiedersehen" but it can happen in shops that the salesperson uses "auf Wiedersehen".