I have the Go and really like it. I can cut only 4 layers of fabric at a time because it is hard to crank; several people said that it gets easier (and you can cut more layers at a time) after it has been used a lot.
The Studio has a lot more dies available for it than the Go, but both the machine and the dies are more expensive. I would love to have a Studio, but you have to have the space to dedicate to it (it's not portable) and the cash to afford it.