I like the tumbler die because it makes a hard-to-cut shape easy, plus it lops off the corners making matching much easier. I also really like the triangle dies (in different sizes) because they also lop off the corners, making matching when sewing much easier. Both of these I would place as 1st tier purchases.
A lot of people love the strip cutter dies, and I have them, but I think a June Taylor shape cut makes these a 2nd tier purchase. I don't always need multiple strips of a single fabric. They are good, though, for when you need lots of strips of the same fabric.