I personally like Johnsons vocals more, Scott was clearly the shit in his day, no complaints from me there, but when I think of AC/DC, I think of Back in Black, dude absolutely killed it. I think he's got a bit more range in his voice, they sound identical sometimes, it's tough to tell them apart if you're listening to a mix between the two on certain songs, maybe that's why AC/DC continued to be successful, either way, I think they both did a great job as the frontman, but I'd give the edge to Johnson, he had the added advantage of knowing what Scott already sounded like