Around here the thoughts are generally:
1. KG is a a punk, TD is a gentleman, he's better anyhow
2. KG sucks in the playoffs
Well, by Win Shares, KG is better than Duncan, not by much, but by a bit (career or peak 10 years), but TD has KG by WS/48 by more.
Win Shares == wins. Everyone knows KG's Wolves were worse than the Spurs. In KG's 10 best WS regular seasons his teams averaged 52.6 wins and Duncans teams averaged 56.5. Run the WS each earned during those 10 years (KG 134.3 > TD 132.6) you get TD contributed 92.2% as much as KG did to his teams wins.
As for playoffs, most of his teams had poor seeding, so they didn't win a lot of games. He also got a lot more attention than Duncan defensively in most cases since his teammates on average were weaker until he got to the Celts.
If I needed a 5/4 I'd take Duncan, a 4/5 I'd take Garnett - can't go wrong either way. I think both are top 14 all time or better.
Malone might have the Win Shares going for him, but his defense wasn't good enough to rank #1 or #2 among PF's (Duncan still has more games played as PF, not at C - and he didn't forget how to play it). I'd take both over Malone or any other PF.