GC can do everything except thick dies (the Sizzix Bigz and Originals, which includes many of the Tim Holtz dies).
BS/BK (same exact machine just different colors), can do everything except the largest of the Grand Nesties.
Big Shot Pro can do everything, but is of course much more expensive.
Holly swears the GC has superior embossing abilities.
For embossing ONLY, the Sizzix Texture Boutique is perfect and very affordable, but it only embosses. I'd lay money that you'd want a die-cutting machine sooner than later
To me, BS/BK is the more versatile because I love a lot of the Sizzix dies, and the Grand Nesties just don't interest me much - partly because of their expense and partly because I rarely have a need to cut anything that large.
If you love the Grand Nesties and don't care about Sizzix, you may prefer the GC.
I have the Big Shot and haven't found much that it won't do!! As the previous poster said, it won't do the largest Grand Nesties, but I have never had a need for anything that large. I emboss, cut Sizzix Bigz, all the thin dies, Sizzlits, it is so versatile. And often on sale somewhere...so not too expensive. All my scrapping group started out with Sidekicks and now we have all moved up to the Big Shot. I also have a Klic 'n Kut but I almost never use it since the Big Shot is so much more convenient.
Well i did get the Big Shot at the Scrap Expo for $59.99. I watched a tutorial on You Tube. The Big Shot can use most of the dies from other companies. Spellbinder can't (to my knowledge).
I have seen the Big Shot for $59.99 all over. It makes me wonder is they are going to come out with a newer version. I bought mine mainly to emboss, but wanted the option to die cut. I do own a Silhouette and the original Cricut.