I have the Fiskars Fuse machine - it can handle both Sizzix and Accuquilt dies, you just have to shim them properly. It took me a bit of experimenting to figure out the perfect shim sizes, but now that I have it all worked out it's a pretty handy machine. It's a very heavy and sturdy machine and I think it cost less than either the Big Shot or Go!. It can't handle the new Go Big dies though - not wide enough. It's the same width as Big Shot or the standard Go! size machine. (Bigger than Go Baby)
I only use it for curved or rag pieces, though. I bought it intending to use it to dice up my scraps into squares and rectangles, but have discovered that for straight cuts, I'm faster and create a lot less waste by using my June Tailor strip-cut ruler and rotary blade. So far I haven't gotten the arthritis curse, but judging from all the women in my family it's right around the corner for me. I anticipate I will use the die cutter a lot more when my hands start to go.