Strategy that’s worked the best thus far:
Kino Der Toten
Stay in the initial room until one person has atleast 1750, and everyone has atleast 1000 points. The person with 1750 open the upstairs room – everyone buy the smg on the wall for 1000 and camp back in the corner of the farthest room with one window.
Once you’re on wave 6 or 7, backtrack to the original room, go downstairs and proceed to open all doors until you reach the theatre. Once in the theatre, if you do not turn on the power – you will have an excellent camping position with one window to defend, while the rest stream from the door to that room / the window next to the door. Using this strategy, you can maximize your point intake prior to turning on the power and the crawling zombies to start attacking.
In between rounds, save a crawler for box opening purposes of course. I have seen many times where the box starts in the theatre and then immediately goes behind the curtain, once the teddy shows his face. If this happens, and you’re without DECENT weapons pre-power on, then you really have no choice but to turn on the power. An unlucky round, as this has only happened to me a couple times.
Using this strategy I’ve made it to 10-11 with about 10,000-11,000 points, turned the power on from there and ran loops around the whole map with upgraded weapons. Once you’ve upgraded to the Zeuscannon you’re next to unstoppable