Props to the OP, this is one of the most interesting questions that doesn’t get commonly asked but is a very good question.
Both Duncan and Walton are two of the highest basketball IQ, most fundamentally sound big men ever.
Obviously Duncan had the better career, but if we’re talking prime for prime pure basketball ability… it’s so very close.
They’re completely a wash on defense. I’d say Walton had a bit more athleticism so he could jump a bit higher for the blocks, but Tim was no slouch so it’s honestly a wash there. Both are also great rebounders, and I’d say they are a wash there as well.
For offense, Walton was the better passer but Duncan I would say was overall more offensively skilled. You put Tim on the block and it’s extremely difficult to stop him. He had of course that go to bank shot but also a reliable hook and great footwork so it was hard to stop him. Walton was more of an opportunistic scorer who rolled really quickly to the basket, or would find a cutter to pass to out of the post, but he wasn’t the type of guy who you relied on for consistent baskets like Timmy.
Overall, it depends what my team makeup is. Do I have other great scorers on my team? Then I’ll pick Walton because he can help make them better and find them easy cuts to the basket. If I don’t, then I pick Duncan because I can rely on him to be my main offensive weapon.