As Oblivious said , the Müllner Brau is excellent , Beer Mecca for me . it really is an experience and the beer is nectar.
Stiegl is the local commercial brew in Salzburg, it's a bitter dry lager as I recall , but not bad at all.
Salzburg is a very commercialised tourist town ( Sound of Music themed , Mozart is the local hero , the local chocolates are Mozart Kugeln . Pretzels are lovely from street stalls and about the size of your head , good for salty treat between pubs. ) But pretty charming anyway . Any pub should have decent beer , But I'm not overly fond of Zipfer . You may have to try different pubs for different beers as tradition in Austria is for single beer pubs , rare to have a big selection.