Urahara Kisuke, though he's the ex-captain of the 12th division he surpasses many of the captains wif his broad and deep network of intelligence and understanding of Soul Society, Shinigamis and Hollows...he also invented the *Hougyoku (Ep.61 explains this)...
He's also a great mentor to Ichigo when they were preparing on to rescue Rukia from being executed, thus his battle skills shouldn't be ignored.
A very mysterious man, *somehow he's been planning everything from the very first episode when Rukia gives her powers to Ichigo, and lent her a special Gigai....till the end of the 'Soul Society Mission'...
He's also the most humorous captain of all... :P
The captain that rivals Urahara is Aizen of the 5th division.