Weighing the options

I'm stuck. And I'm not sure how to figure this out. I teach AP Biology. Last year was my first year and I just picked up someone's curriculum and taught it. Well, this summer I'm trying to be more mindful in my teaching and so I'm planning ahead. One of the projects is to create an AP Biology curriculum that is mine. The problem I'm running into is the sequence. Last year I taught macro to micro, so evolution first and then we worked our way down to cells, interactions, etc. That is definitely one way to go and lots of teachers do it that way. The other way to go, and what I thought I would do this year, is start with chemistry. Give them a basis for what is going on then move into what is happening with evolution and all that stuff. Now both ways are legitimate and teachers do it both ways, I just can't decide what is best for me. One one hand I feel that giving them the big picture and then explaining why it happens (evolution first) makes more sense because we can constantly refer back to the effects of what we are talking about.  On the other hand, teaching chemistry first gives them a basis to understand why something happens and then we go into the effects of those things. They both make sense in my mind and I can see the validity for each. But which one do I want to do first? 

Now that I've laid it out and given it some consideration, I think I'm going to stick with evolution first. To me, that just makes more sense. We get the big overview of what is happening, evolution, then we go into the details as to why. Also, evolution is a fairly simple topic to start the year with so it kind of slowly eases them into AP.

Sometimes all I have to do is write it out.