Google Now vs Samsung S-Voice – YouTube.
Comparison Video of Google’s Voice Help System (Google Now available with Jelly Bean) and Samsung’s S-Voice (available on the Samsung Galaxy S III.)
See how Google Now on the Galaxy Nexus running stock Android Jelly Bean compares with S-Voice on the Samsung Galaxy S III running Ice cream sandwich with Touchwiz Nature UX.
I think it’s pretty clear that Google Now wins!