First of all, I am going to disagree with everyone here and say that I think it is cool that you have a family that includes you in the household decisions.  When I was your age, I'm sure that my parents would have at least asked my opinion about a move.  They probably wouldn't have left the decision to me, and they probably wouldn't have given me money directly, but they would have included me.  They are treating you with the respect of an adult member of the family.  Families help each other out, and families make decisions together.  Personally I think it is great that they are letting you have a say in the matter.  While you still may be a child, you have to start making decisions on your own eventually.  Your parents will let you make a decision on where to go to college, so why not have a say in this?
Getting to your question, I would pull up stakes and move to AZ.  I didn't stay in touch with any of my friends from high school in college, so from my experience, I don't think your current group of friends will matter much in three years.  Also, you can and will make new friends when you start as a junior next year.  When you graduate, you will have the option of going back to Michigan, or staying in Arizona.  The weather is much, much better, though the summers are much hotter.  Finally, there is the money issue.  This is very important as you'll be able to buy a decent car with that money that you can take along to college.
Ryan