To win, i found the best way is to max out skeletons (warriors and archers) all the passives, and get diablo as high as possible. Thats all you should need to use. Zombies, other creeps and hero are relatively useless. Alice can be useful though, but dies to easily in the final stage.
tip, rush as hard as you can, then use the bombs, then send more guys... if this fails, you did it wrong, focus on on area, top or bottom, and destroy one spawn at a time