Who’ll succeed Microsoft's Steve Ballmer?

The candidates outside Microsoft to succeed outgoing CEO Steve Ballmer are impressive, management expert Jeffrey Sonnenfeld said Friday.

His top pick is T-Mobile CEO John Legere.

Legere, a former executive at Dell and AT&T, is experiencing "incredible performance," Sonnenfeld said on CNBC's "Fast Money."

"John Legere knows every part of this business. His ad rates are soaring. At T-Mobile, the usage is up dramatically," he said. "And he actually really knows the device business. His relationships with Apple, Samsung and everybody out there is spectacular."

Two other possibilities were Yahoo's CEO and Facebook's COO.

"Marissa Mayer should be on everybody's short list. It's incredible what's happening at Yahoo," he said. "And, of course, Sheryl Sandberg is certainly dressed up and ready to go as CEO somewhere, too. So, there's ample, fantastic talent on the outside."

Ballmer, who succeeded Bill Gates to take the helm of Microsoft in 2000, announced that he would be leaving the company within the next 12 months.

(Read more: Microsoft CEO Ballmer to step down within 12 months)

For his performance, Ballmer eared a "B-minus" grade from Sonnenfeld, who is senior associate dean for Executive Programs at the Yale University School of Management.

"Over that 11 years, he's actually tripled revenues," he said. "It's a $76 billion business. It was a third of that when he stepped in."

During Ballmer's tenure, Microsoft returned close to $200 billion to shareholders.

"Nobody else has given shareholders that much back in dividends and repurchases," Sonnenfeld said. "That's a pretty good record."

(Read more: 'Get out, step back' from Microsoft: Mike Murphy)

Sonnenfeld also praised Microsoft for evolving into new areas.

"They have 75 percent of their revenues now are not coming from those old operating systems," he said. "They've been moving into these new business categories."

Even though—as TheStreet CIO Stephanie Link noted earlier—Microsoft stock is 39 percent lower since Ballmer took over, Sonnenfeld said that share prices weren't everything.

"Let's think of those new-new thing companies," he said. "The companies that were being celebrated then for their soaring stock performance were, you know, GeoCities and Excite and Lycos and Kozmo and WebVan and HomeGrocer and Netscape, Snap, Lycos, eToys.

(Read more: Markets ready for cyberthreat: Former FBI expert)

"What's happened to those? They were soaring stock and then they disappeared. This is a company that's built for sustainability, not to be the new-new thing."

Sonnenfeld said that there was "a dependability" and "a reliability" with Microsoft's moves.

But why now?

"The why now issue, I think, has to do with why would this not been about six, seven weeks ago," he said. "If there was great board disaffection, you would not have let him go through this massive restructuring. What he's done now is the heavy lifting for a successor. He said he wasn't going to see it through, sort of like Moses saying, 'I'm not going to get you to the Promised Land.'"

By CNBC's Bruno J. Navarro. Follow him on Twitter @Bruno_J_Navarro.

— CNBC's Stephanie Landsman contributed research to this report. Follow her on Twitter: @StephLandsman.

Trader disclosure: On Aug. 23, 2013, the following stocks and commodities mentioned or intended to be mentioned on CNBC's "Fast Money" were owned by the "Fast Money" traders: Stephanie Link is long AAPL; Stephanie Link is long GS; Stephanie Link is long JPM; Stephanie Link is long WFC; Stephanie Link is long CSCO; Stephanie Link is long FB; Stephanie Link is long EBAY; Stephanie Link is long GPS; Stephanie Link is long F; Michael Murphy is long BAC; Michael Murphy is long C; Michael Murphy is long FB; Michael Murphy is long F; Jon Najarian is long AAPL; Jon Najarian is long GLD; Jon Najarian is long JPM; Jon Najarian is long MSFT; Jon Najarian is long TSLA; Jon Najarian is long EXPE; Jon Najarian is long QCOM; Erin Gibbs is long AAPL; Erin Gibbs is long MSFT; Erin Gibbs is long M; Erin Gibbs is long GPS.