I was struggling between those two, and I just decided to buy ES yesterday because I just needed to be done with it! I have looked only through the teachers manual so far and I am pleased. OF course it is always different once you start using it. I think both are equally good resources. I really was going to plan my own biology since I have the college classes and lots of resources, but I am not a "hands on" science person and I was overwhelmed with the logic stage and all the experiments. So, we may just use this an a guideline. I will be making my own lessons with my younger son, but will follow ES so that both boys are doing the same thing. I don't plan to do much if any of the human body as my oldest has spent all this year on that. So, we will spend more times studying animals as a week is not enough for us. Long story, but I too hope that we can stick with this choice for the next few years!