I recently wrote an article on this:
how-to-pick-a-recommender-129379.htmlThe best recommenders are going to be those that will first and foremost give you a glowing recommendation. Assuming that all your options will, it would be best to chose someone that is quite familiar with your work product, and has been your direct supervisor at one point or another (or now) or your direct supervisors supervisor. If you are young and lack much experience, then it is possible to chose an achademic (aka teacher) recommendation, as long as they are also familiar with your work product. Outside of that, think about people that are older than you, have attained strong career growth and achievement, will always be around and care about how you progress in your career, and get them on your team. Make sure to coach them up a bit, and remind them of certain aspects you'd like to touch on (maturity, leadership, communication, dependability, etc..) and remind them not to make it too informal or formal but to instead toot your horn a bit. You want them to make it seem like you are the best candidate out there and that this school should choose you over everyone else!
I wouldn't recommend switching it up too much if you don't have to. I would pick the absolute best you have, and use them for all (so you know all applications are equal). Often times schools have forms to have them fill out to help them with their recommendation so it is easier then one may initially think it will be.
Good luck to you!