My Oktoberfest advice is: go early. On weekends that means 8 or 9am. I found that without a booking there was no chance of getting in anywhere for a drink after that.
In town, the Ayinger[/url:2pv5ub9s] and Schneider[/url:2pv5ub9s] beerhalls are recommended. An escape from the Big Six brands too. Both are central.