My personal reasons for the BSP over the GO (I have had both-sold my GO)
1. can use way more dies in the BSP. That was the main reason I switched. I wanted to do a 10" square and there's no way for that to ever happen in the GO. I can use my old GO dies as well as sizzix/ellison dies and if I want to, most studio dies.
2. easier for me to crank. I had serious shoulder issues after using the GO only a couple of times and none at all with the BSP.
3. the BSP is so much more solid than the GO. On the flip side, it is 50 lbs and has to have its own dedicated space. Not a problem for me since we made a cart for it but it could be an issue for people with limited space.
#1 sewed it up for me. I hate when companies go all proprietary (which is why I have an android phone but that's a subject for another thread).
On the other hand my sister has the regular size GO and is happy with it. She travels from Alaska to the lower 48 a couple of times a year so she likes portability.