I have an Accuquilt Go! and like it. People who do a lot of quilting and have the space for it really like the Accuquilt Studio.
Recently here I have seen that some people prefer the Sizzix Pro (may have to do a search to get the correct version of the Sizzix machine). They say it is heavier duty than the Go! and has the advantage of being able to take both Sizzix and Go! dies. (The Go! is limited to Accuquilt Go! dies.)
Probably the first thing to decide is how much space you have available. If you are tight on space, then the Go! is probably the best choice. I like the way I can fold it up and tuck it out of the way when I'm not using it. The Sizzix is portable too, I think, but considerably heavier for moving around. The Studio needs permanent space.
The second thing to decide is what your budget is. The dies probably add up to more of an investment over time than the cutting machine itself.