Basketball-Reference.com has advanced basketball statistics (newfound statistical analysis is not unique to baseball alone). Last season alone, Lebron had more defensive win shares, 15.3 to 12.7 (almost a full win), and a lower DRating at 104 to 105.
Win shares are similar to baseball win shares, with each share 1/3 of a win. The DRating is how many points allowed per 100 possessions, so lower is better.
To my eye, Kobe is better on the ball with Lebron being better at off the ball team defense. Like their offensive contributions, Kobe is better as an individual while Lebron is better as part of a team. Last I checked, it is still a team game.
And, Kilo's point is a good one. Pierce torched Kobe compared to what Lebron allowed in their matchups. I would expect the best perimeter defender to not allow Pierce to get to the hole as easily as Kobe did.