Well, in general, the benefit of moving to 32-bit boards is a massive CPU and memory improvement. A lot of the tiny 8-bit boards that the printers currently use are hugely limited by slow single core CPUs and very limited memory. Most of the firmwares available for these small boards have already maxed out all available space, so it's hard to add new features without removing something else.
So that's a high level answer for you.
I've probably tested 10 or so different firmwares myself - Sprinter, Marlin, Repetier, Sailfish, Smoothie, grbl, etc. While I am excited for a year from now when we will (hopefully!) have many stable 32-bit firmwares available, from my testing I've encountered a lot of bugs and issues with the smoothie firmware. It's not unexpected for a new firmware like that, as they are blazing some new territory there. Personally, I decided to stick some something that is more tested and stable like Marlin for now. From my testing it was hard to see any noticeable quality improvement from Smoothie vs Marlin, so I decided to go with the more stable one.
Just my $0.02
