I'll vote for Jeff Fisher because out of the teams listed, the Titans were expected to win the least amount of games according to season win totals at pinny. Its not like the guy has a team full of all pros or even one pro bowler to work with and has gotten the most out of his squad. They started the year off as everyone expected and as soon as Vince became the full time starter things started changing.
Other choices pretty much had some all pros such as Brees, Horn, McCallister, the drafting of Reggie Bush. Diego had LT, Gates, Merriman. Chicago, everyone knew they would be good playing in a weak division and having a cupcake schedule and a great defense. Mangini another good choice.
If the Titans make the playoffs Fisher probably gets it, otherwise Payton probably wins, which is well deserving also.
Fisher
Mangini
Payton