First year we stayed at First G hotel near the central station, very good location and easy access with trams.
Second year we stayed at Linneplatsens vandrarhem and hotell, had a huge balcony in our room with views to Slottskogen, the con was after the main festival close you might get lazy and dont bother go to Stay out west, especially if the weather is shit :)
The other years we stayed at a friends flat in Johannesberg
Is a good guideline