If you only want to stay in one base town for your whole trip, it really depends on what you want to see. You can't feasibly see Bavaria from only one base.
In my opinion you could divide Bavaria into three general areas to be seen from three different bases - one in the north (we recently spent a week near Bad Windsheim and visited Rothenburg, Nordlingen, Bamberg, Nuremberg, Schwabisch Hall, etc as day trips), one in the south west (from which you could see Munich, Neuschwanstein, Mittenwald, Oberammergau, Wieskirche, Andechs, etc as day trips) and one in the south east (from which you could see Herrenchiemsee, Berchtesgaden, Salzburg, Burghausen, etc as day trips). All these areas could overlap a bit depending on where you choose to stay but it would be tough to see them all from one base.
Personally, I'd recommend choosing at least two bases.