Well as you suggested tower leadership as top tier tower people, possibly also tower intelligence for the mods in
the tower. The next few would depend entirely on what stat tracking abilities you have, maybe we set thresh holds for the other ranks, eg if someone has grown over 50 wheat they would become part of the "Tower garden team" or if they had gathered so many resources they would become "Tower Recon Team" Also "Tower Defense Team" coul be a good rank for people with so many kills on Z's / mallers.