Eiffel tower is worst unit. Auto-clicker is best unit.
After the first wave, I realized it was just about how fast you click, so I turned on an autoclicker and left the mouse still and got to like wave 8 or so before experimenting with other things just to see them, but didn't really have to. When you just click a handful of times, the towers pose a threat, but when you just spam as much as you can in the spawning window, they barely affect anything.