The nexus is great and I would not discourage you, but the SGSIII is more feature rich at this point, especially if you put JB on it.
Just one feature alone make the grade for me. I can shoot a video, and snap 10 pictures at the same time.
I know a lot of people do not see that as a real upside, but combine that with the other features out there, it puts the SGSIII ahead of the Nexus.
If you have a month, see what happens with the next Nexus.