I value defense way more than offense. Duncan was a better defender than Malone.
As to efficiency... it's a shame that B-R.com's shooting statistics only go back to 2000-01, because I'd be interested in seeing those numbers for Prime!Malone. B-R.com indicates that, from 2000-01 until he retired, 80.4 percent of Malone's 2-point attempts and 85.7 of his 3-point attempts were assisted, compared to 54.6 and 78.6 percent for Duncan. Now, obviously Duncan played almost his entire career with that as a recorded metric, and Malone only played the last four years of his career with it, but seeing as how Malone played something like 97 percent of his career with the all-time career assist leader, I'm not inclined to assume that his career numbers would be much lower than 80.4/85.7. I am highly doubtful that the number is even below 70 percent, let alone below 60 percent; it's probably somewhere around 75 percent, for his career. And well... when you're getting spoon-fed for three-quarters of your shots, I would certainly hope that you can be efficient at it.