In the abstract, the last thing President Obama needs in a new FBI director is another (very) tall, white, male moderate Republican. But there are people who compel you to throw out the rule book. And Jim Comey is one of those people. President Obama deserves a lot of credit for choosing him as FBI director---assuming for a minute that the current spate of news stories is correct.
Comey is a friend, and he is a friend of this site. He is also, speaking objectively, a near-perfect candidate to run the FBI.
Here's the easy part: A qualified director of the FBI needs to have significant managerial experience in law enforcement. These days, you particularly want someone with a real intimacy with national security investigations and counterterrorism cases. You want someone who knows the bureau and can command the respect of its famously insular culture. You want someone with that ineffable quality of great leadership. And you want someone who somehow projects an anti-Hoover-like incorruptibility. Put this all together, and the easy part is not at all easy. There are very few people who truly have all of these qualities---and Comey is one of them.
But Comey also has an additional quality that makes him a unique candidate for the position---unique not just now but over a very long time. To be a successful FBI director, you have to be someone the public believes is truly independent, someone who will follow the facts wherever they go, who will investigate other members of the administration in which you (sort of) serve. The public should even believe that if it came to that, you would stare down the President himself over compliance with the law. It requires highly specialized circumstances to establish this particular quality beyond a shade of public doubt---and most people, fortunately for them and for the public---never have the opportunity to do so. But Comey did have this quality of his leadership tested---and in an episode initially secret, and now famous, he showed himself capable of looking a president of his own party in the eye and telling him that he would resign unless legal problems in a high-stakes classified program were fixed. Nobody, including Barack Obama, can now doubt for a minute that he is capable of doing what needs to be done and telling the president the painful truths he may need to hear.
For which reason---again, assuming the stories are true---this is a great decision by the President, one which Congress should ratify as quickly as possible.