I have the Go and the Studio at home, and the Studio at work. The die that we use the most at work is the tumbler. We have a 4" tumbler (with 6 cuts on a board) and a 7" tumbler (with 4 cuts on a board). At home I have the "nesting die" that can cut 4 different sizes of tumblers, but only one cut at a time.
The thing I wish I could do is to buy dies with several of the same shape on a single board. Like one that has 8 5-inch squares, so I could cut 8 X 8 layers = 64 squares with one pass. It takes just as long to cut by rotary cutter as it does with a single shape on a die.
It's fun to have custom dies made, too. I had some made for my home business, and octagons for my Denim Stars quilt. I want to have some miniature Dresden plate dies made, to cut the scraps that are leftover.