Moin, moin is used in the North of Germany. I 'd say that Guten Tag is possibly more official (e.g. when being customer in a shop, whereas friends you would greet with Hallo as Thekyr mentioned already. Grüß Dich and Grüß Gott are not only used in Austria but as well in Bavaria (but anyway Bavarian German has quite some things in common with Austrian German).

Many also simply say "Hallo", similar to the English "Hello". I think "Grüß dich" or "Grüß Gott" is more commonly used in Austria, than in Germany. (At least that's my impression being an Austrian) It sounds rather oldfashioned too. On the other hand, I don't think "Guten Tag" is that oldfashioned.

still could hear that everyday, so either that is not old fashioned , or i live in a old fashioned town . somebody will say god bless you too, but seldom heard that till now . only once , for one moment , i did not know how to answer that actually.

"Guten Tag" is an every day greeting. "Tag" is used as a greeting but sounds less formal.