I wanted to put KG on top but Shaq and Timmy has clearly dominated this era(year-by-year, NBA finals featured either of the two before Boston's championship)
I guess it really depends on whether you feel you can separate the individual from the team in these kinds of lists. The normal standard (which I generally agree with) is to weigh championships heavily in this type of comp. But I almost feel like KG is a special case, simply because the gap between his teammates and the teammates of Duncan and Shaq is so huge over the decade that it can't really be ignored when comparing the individuals. Plus, the only times that KG has had even a hint of teammate talent his teams have been on top of the league barring injury.
If you can be convinced to try to judge the players as much as individuals as possible (which is, admittedly, a hard sell), then Shaq vs Duncan vs KG for the decade becomes extremely close. I put together a few ways to try to judge players at least somewhat objectively against their peers, and KG scores well.
Finals MVPs: Duncan and Shaq both have 3 this decade. This is what usually separates them from the pack in this type of comp. Of the individual awards, though, this is the one that is most team-dependent since the pool of possible picks only comes from the Finals teams. But this does give Duncan and Shaq the early lead here.
Top-3 MVP finishes this decade: 4-way tie between Duncan, Shaq, and KG (Kobe is the 4th) with four top-3 finishes apiece (Dirk is on the next level with Nash at three top-3 MVP vote finishes). Duncan has two wins (both close) and two seconds. KG has a win (blowout), two seconds (one close), and a third. Shaq has a win (blowout), a second (close) and two thirds.
All NBA/All Defense teams: Duncan (7 1st team All NBA, 7 1st team All Defense) and Shaq (7 1st team All NBA) lead this category, but KG isn't far behind (4 1st team All NBA, 8 1st team All Defense). Plus KG got his DPoY, which I guess is on about this level for individual accolades.
Advanced stats - PER: Again, Shaq, KG and Duncan are about tied for the decade lead. Shaq had the highest yearly scores from 2000 - 02, but fell off a lot over the decade. KG had the highest power forward PER ever recorded in 2004 and was pretty consistent over the decade. Duncan was the most consistent over the decade.
Advanced stats - Net +/-: 82games.com didn't start keeping this stat until 2002-03, which hurts Shaq since it missed his dominant days. Since the 02-03 season, though, KG has dominated this stat more than anyone in the league. He led the league 3 times (twice outright), including the highest net +/- 82games ever recorded for the 02-03 season. Duncan led the league twice, once outright and once tied with KG (07).
Advanced stats - Wins Produced: Dave Berri wrote a detailed article comparing Duncan and KG with this stat in 2007, and concluded that KG produced more but Duncan's teammates produced more
http://dberri.wordpress.com/2007/05/15/speeding-up-time-for-bill-simmons/. He did a similar comparison with Shaq and David Robinson
http://www.wagesofwins.com/RobinsonShaqWP.html. Looking at all 3, by this stat KG produced the most individually, followed by Duncan followed by Shaq over the decade.
Advanced Stats - Wins Above Replacement Value: Basketball Prospectus writer Kevin Pelton ran his stat for the decade earlier this year, and found that Garnett was on top followed by Duncan, then a huge gap until the next group led by Kobe/Dirk/Shaq.
http://www.basketballprospectus.com/article.php?articleid=532Bottom line: There are so many "advanced stats" out there these days that we could go through various stats ad nauseum. The point is, by almost any systematic comparison that even tries to look at individual player impact KG is right there with Shaq and Duncan for this decade, if not higher. Yes, Shaq and Duncan have more championship hardware, and if that is your criterion by all means they will be 1-2. Before 2007, any argument for KG would be weakened because he had NO team hardware. But now that he has actually proven that he could win a title with reasonable support, to me it really re-opens the debate for the decade, because he already had the individual numbers and accolades to compete with the big dogs. Now he has some team chops as well.