This is Obama's time to not worry about the politics of re-election as he won't be seeing another one. He needed to say "hi, the people picked me and this is my guy", which is exactly what he did and good on him for it. He needs to pick who he's most comfortable with to maximize what we get done the next few years.
I believe that Barack Obama should nominate Chuck Hagel for that position. Hagel would do well as the Secretary of Defense. He is an experienced politician that has excelled in various positions over the years. Hagel would succeed and I think he would do a better job than most of the other people being mentioned as possible candidates for the job.
Chuck Hagel is an experienced politician and is well versed on military affairs. He served as an enlisted man in the U.S. Army in Vietnam during the war. He is a well educated individual and would be good for the position. He may be less likely to get the country in a war than some other possible nominees.
He should not have been nominated based on the fact that he so openly supported torture in the past, under George W. Bush. Torture is a disgusting practice and shouldn't be supported in any circumstances and anyone who has been for it in the past does not deserve to be promoted in the present.