I have the Westminster Edition one. It's as good or almost equal to the Accuquilt Studio.
Now I have used the Big Kick, Westminster, the AccuQuilt Go and now the Studio. There are pluses and minuses for each one depending on what you want to do.
I have used the Sizzix Big Shot Pro Westiminster Edition quite a bit and love it and have even used the GO dies in it however I must warn that I guess there is a reason each has it's quirks. Although the GO dies will work and cut on it you have to adjust higher or lower the padding to be able to cut and if not careful you can ruin some of your Go dies but than again I have purchased the Big Shot Dies for and they are made even cheaper than the Go dies. I've bought some of the Big Shot quilting dies and for the money it is not worth it. Stick with the Go dies.
The best dies are the Studio ones because they are made of wood, foam and blades. Also the studio dies depict the photo on reverse wooded side.
Now as far as which machine cuts the best and with great ease it is the Studio one and even the Westminster can't compare to it.
I have found also the pads for the Big Shots get used up much faster and are more prone to breakage over the Go or Studio pads. The Studio pads are acrylic like the Big Shot but seem to be a better quality. The Go pads are sort of a rubberized and seem to last much longer.
If pricing is what you are determining on I say get the Westminster over the Go machine unless you want to be able to carry it with you around the house or to guild meets.
My having waited and negotiated when I bought the Westminster last year I was able to get it for $258 which included shipping.
A couple weeks ago I was able to buy the Studio for about $350 with free shipping. I bought it because I could not resist the price and also the fact that it has dies I wanted that can't be used in other machines.