German greetings tell you where you are:

Word	Meaning	Where
Moin	hi — at any time of day	the north
Grüß Gott	hello — a little formal	the south, Austria
Servus	hi and bye — informal	Bavaria, Austria
Grüezi	hello	Switzerland
Tschüss	bye	the north, and widely elsewhere
Ciao	bye	everywhere

Guten Tag and Hallo work everywhere. In the south and in Austria you'll hear Tschüss less often than Servus — or the Bavarian Pfiat di, bye.