As i see here, GT 630M is slightly faster in general, and faster in some games. At certain games though hd 7670m leaps a little ahead of GT 630M. IMO they have identical performance. Depends of what games you will prefer to play.
Have a look at this chart:http://www.notebookcheck.net/Mobile-Graphics-Cards-Benchmark-List.844.0.html
The chart shows 7670M a little better than GT 630M but in real, they are similar in performance. So whatever you choose, won't be the bad choice imo