consensus seems to be overwhelmingly in favor of lower.
I agree with that.. and I also agree with swag that really only 1 tower is necessary (under rax) assuming your ally gets there before enemy starts upgrading their tower outside of 12.
only reason to make 2nd tower is if its obvious they're going to make forward progress into 12.. I'd prefer 2nd tower in that situation to be located under gold mine (on the right side) or under the hall if it was clear the tower needed to be heavily defended.
the towers under the gold mine have some serious flaws .. they don't attack enemies towers under 12 entrance, which means the person occupying 12 is defended, but unable to make any type offensive attack until he makes a cat to eliminate the enemy towers, and is forced to repair his own barracks while waiting on the cat that he never should have had to make begin with.
so he's trapped in his base.
forced to spend res on a cat
forced to spend res repairing instead of collecting resources.
can't make grunts out of rax on right without grunts taking hits by enemy tower... while cat is being made in rax on left.