The best strategy seems to be to use those rocket launchers. A better strategy is to have a booster tower in the middle surrounded by rocket launchers. The latter is difficult to get right but works well. You are bound to squash all creeps if you do this
My strategy was to build the maze to funnel aliens into one singal route and then maximize the length of the route from begining to end, then focus on upgrading or buying towers with longest range (centrally located included).