Now that Elizabeth Vargas and Bob Woodruff are co-anchoring ABC's World News Tonight, three networks have refilled their nightly news anchor chairs in little more than a year. Let's see how well they're doing.

ABC Vargas and Woodruff have been leapfrogging from country to country on separate assignments. Wouldn't it be cool if they could pop into each other's segments, like Bewitched? All in all a smooth, forceful dynamic.

NBC Brian Williams, Tom Brokaw's replacement since late 2004, is the ratings leader. The fact is his delivery is terrific: crisp yet informal, casual yet authoritative. The voice draws in the ear before the eye.

CBS Bob Schieffer, who took over from Dan Rather on The Evening News in March, has a nice, unemphatic way of working through the headlines. CBS reportedly wants to give the job to Katie Couric. But transforming a sunrise power into a sunset one might cause a solar eclipse. So go careful there.