I think he'd have been great but I don't think better than Nicholson, Nicholson was amazing as the Joker.
I wish he could have played an older Joker for a Dark Knight Returns adaptation.
He most likely would have acted more like Joker instead of Nicholson relying on his role in The Shining.
I'd also ask for the people who think Jack does a better job, how would you know if he was a better choice than Bowie?
I'm curious, for the people who think he would have done a better job. What do you think Bowie would have done to outperform Jack? Keep in mind, the writing would have been exactly the same.