Be aware that the Accuquilt Go! (which is their portable die cutter) is now available in an electric version so you don't need to hand crank. Both of these versions are lightweight and compact so they are easy to store.
The Accuquilt Studio is wonderful if you have a dedicated space where you can leave it set up. This is the one that quilt shops buy to crank out kits because you can cut so many more layers of fabric at one time (and easier to crank for the same number of layers on a Go!).
All I know about the Sizzix is what I have read here. You can use dies from a variety of companies in it, but will need to be willing to add shims when necessary.