Marc Hirsh

As The Voice returns to NBC this week for its fourth season, viewers are seeing two new, if quite familiar, faces as Shakira and Usher occupy the coaches' seats vacated by Christina Aguilera and Cee Lo Green. Its talent-show rival over on Fox, The X Factor, will also see two new judges when (if? no, "when," surely) it comes back in the fall.

So why does The Voice seem so healthy and The X Factor so wobbly?