Well, it depends on what your motive is. If you want everyone to be on " equal footing" then I would suggest a circle, where your exec board is mixed in with the crowd. If you want to have a little more exec board presence, then all sit together on one side of your circle..
If you really want to establish boundaries of power, then line 'em up.... and have your exec board face the crowd, and have the guest in the middle of your exec board line....
What it the best formation of tables so that you are not too far away from eachother AND so that no ones backs are towards eachother? We are expecting around 30 as we are having the new food services director coming to the meeting to explain menu changes (might get ugly).