WAS and AAM have enough units that using shapeways other other models/cards like team poseidon that you can have whats fairly close to a complete game.
Something like MechanizedWarfare suggested works best; US & UK vs GE usually works well. A free-for-all is interesting to do sometimes, but often it simply ends up with two players joining up against the third who doesn’t have a chance.
We usually play the 3 wide x 2 deep… but we don’t usually have a large enough table for more than that. I prefer the 3 wide because it spreads out the armies and allows more room for flanking.