IMO, there should be two lists, one for posts and one for perimeter players. I'm not going to try to rate the old timers, but here are my comments on those who played in the last 15 years. I weight team defense heavily, especially for posts, but one-on-one defense is also important. Being a great defender every night (not only on demand) is big. Longevity is a factor, at least in the sense that I want to see several years of great defense ideally spread across more than one group of starters.
Duncan is easily the best help defender and probably the best one-on-one defender. He's got the individual and team stats to prove his case. If you need someone around whom to build your defense, this is the guy. Garnett was very good, but still second to Duncan. Aside from Garnett and Duncan, the only other guy I would nominate as top ten all-time defender is Ben Wallace. Other top defensive posts recently are Marc Gasol, Joachim Noah, Dwight Howard, and Marcus Camby. Ibaka needs to develop his one-on-one defense some, rebound better, and then do all that for several years.
On the perimeter, Bowen had the best feet of any defender I've seen (both in terms of moving them effectively and crane-kicking Wally Sczerbiak). Battier, Artest, and Allen are very good, but I'm not sure they are truly pantheon-level defenders. Non-Spurs fans won't like this, but Manu Ginobili holds the second highest DRtg ever among perimeter players. His off-the-charts BBIQ puts him in the elite status even if you won't hear the idiots on ESPN talking about his defense. Paul George, Kawhi Leonard, and Draymond Green can be all-timers if they keep playing at this level for a few years.
There are a lot of really good players who don't crack my lists because they either expend so much effort on offense that they can't bring the fanatical effort required for elite defense every night (Lebron, Kobe Bryant) or they are overrated based on name recognition or flashy stats at the expense of playing good team defense (Chris Paul, Russell Westbrook, Rajon Rondo). Any of those guys I mentioned are insanely good at times, but not consistently enough to be an all-timer.
