I like Nockstein a lot. Short yet intense – but only if you pick the steep route #70 starting on Wolfgangseestraße. It is a good after-work or morning hike, as the mountain is located just outside of Salzburg (15 min by car from the city center or 20 min by bus #150).
The total ascent is just around one hour (depending on your stamina), but the views of Koppl and Salzburg are quite decent. From Nockstein, there is a direct path leading up to Gaisberg. It is definitely worth taking if you fancy medium-intensity strolls in the forest. Top-to-top the hike takes around an hour as well.
If you are considering Nockstein, but have a little more time to spare, feel free to pick to remaining routes starting in Winkl.
Be careful while going down – the steep path leading through forest can be quite tricky (watch out for roots and small stones!).