There are 2 models. The regular GS and the GS adventure. The Adventure has a larger fuel tank and is much taller then the regular GS. It also only comes with the spoke wheels.
I have a 2015 GSA that I bought new. It has 32K on it. I have not been kind to it and it has been absolutely trouble free. It's been dropped, jumped and dragged thru all sorts of stuff. I've done a couple BDRs with it and have done several multi day road trips with it. I have several bikes, this one would be the last one to go because I can literally do all the types of riding I enjoy with it. There are subtle differences in the options on the 1200. For example the last year 1200 has the TFT screen and even more so with the 1250. The 1250 has a little more power and the newer TFT screen.
I've done a month riding the 1250 and the only thing that was a big improvement over the 1200 was the TFT screen and thats just because it is easier for my older eyes to see.
2016 is a good year, it will have cornering ABS, it should have shift assist and keyless with the analog guages. All years of GS/GSA are available in a low seat/ low suspension option as well, there is a big difference, so if bike height is an issue you might want to look into that as well.
I really didn't want to like the GS, then I rode one for 2 weeks and couldn't believe how good it is. There really is a good reason you see so many of them on the road.