Paul Pierce has pretty much shut down every single SF in the playoffs at the most made them completely underperform. By far the best defender this playoffs in your list, and I might even argued he should be considered the best defender in the playoffs period. Not that he is the best defender, but you can't deny the results of what he has done against Marvin Williams, LeBron, and Prince (who was the hottest player for Detroit coming in to the series).
Pierce has a great argument but I'd go with Bruce Bowen.
First Round - Shut down Steve Nash.
Second Round - Switched onto Peja Stojakovic in Game Three, Bowen proceeded to take him out of the series. The Spurs won four of the final five games because of the Hornet's offensive woes without Peja's scoring.
Conference Finals - Limited Kobe Bryant brilliantly.
Prince and Marvin are worse than any of the three Bowen faced.
I think Bowen did a better job on Kobe than Pierce did on LeBron by a small margin. I could fully understand others disagreeing considering Bron's poor shooting percentage versus Bryant's quality shot making. My chief reasons - Bron shot almost 12 FTs a game against Boston, Bryant had 11 FTs for the whole series. Bowen did a much better job keeping Bryant out of the paint and off the line. Bowen also limited Bryant's playmaking. Bron on the other hand was huge in dictating play and setting his teammates up, he wasn't scoring efficiently but he was making lots of plays for his teammates ... unlike Bryant. Pierce did a better job limiting Bron's scoring but I reckon Bowen did a better job limiting the Lakers offense with his defense on Kobe. That means more to me.
No way Bowen did a comparable on Kobe to what Pierce did to LeBron, especially when you consider how Kobe coasted for the most part in the first half of games without pushing the issue, and when you consider how strong LeBron penetrates, he's easier to foul than a Kobe is. LeBron was pushing the issue way more than Kobe did. Kobe had his way with the Spurs, anyone thinking otherwise is living in denial... forget about the low free-throw shooting attempts, what good does that do for you if he's still scoring so much at such a high percentage? Low FTA, you know what that tells me? That people were giving him easy looks and weren't really contesting his shots as they were supposed to.
Like I said I fully respect anyone's opinion that Pierce did a better job on LeBron than Bowen did on Kobe. I disagree though.
I don't think you're giving enough credit to how severely Bowen's defense limited the Lakers offense. Look at their assist percentages against San Antonio to their regular season average or previous rounds. Lakers went from about 67% in the playoffs, 60% on the season, down to 45% against San Antonio. Look at how severely Odom and Gasol struggled to score, scoring 26 combined points a contest, both shooting their lowest percentages of the playoffs. Then look at the added struggles the Lakers shooters had. Sasha, Fisher, Walton all struggled because Kobe wasn't able to get them good looks.
The Lakers are averaging 105ppg overall in the playoffs (including the Spurs), 108ppg on the season. They were down to 93ppg against San Antonio. It wasn't just pace. The Lakers got more shots up against San An than they did against Utah but less than Denver, roughly in between the two.
The vast of majority of all of that happened because Bryant's playmaking was taken away by Bowen. The Spurs defense was exceptional on LA and on Bryant in particular.
Here's another one from their respective series:
Against San Antonio, Kobe scored 1.22 points per shot
Against the Celtics, LeBron scored 1.21 points per shot
Add in the playmaking advantages (double the assists Bron to Kobe, would have been higher had Bron's teammates not messed up so often) and how much LeBron facilitated his teams offense versus Kobe not doing so.
That's why I give Bowen the advantage. Again I can fully understand why others would go with Paul's job on LeBron. Just felt like adding the turnovers. Pierce did a much better job of forcing Bron into turnovers, 5.3, to 2.4 from Bryant. Pierce did fantastic work.
And guarding Peja, is that a joke? All you need is a guy to stick to him consistently, and you'll have a high chance of containing him, plus his decision making in the later half of the series was simply putrid... he played himself out of the series.
This is exactly the same as guarding Marvin Williams or Tayshaun Prince. Except Peja is a better scorer and better shooter than both of those guys. I don't understand the complaint.
Bowen played exactly the type of defense that bothers Peja and it worked. Nobody on Dallas could. None of the other Spurs could. Peja lit them all up like he did to many through the regular season. Bowen did a fantastic job on him. His D swung that series. I fully believe that would have been a New Orleans victory march without Bowen switching onto Peja and shutting him down.