In my opinion, it is this debate between Tyler Cowen and Erik Brynjolffson. The speakers, the moderator, and the audience questions were all top form.
Remind me never to get into a live debate with Tyler. I thought he was more persuasive at this event, even though I was on Brynjolffson's side at the beginning.
My take on the substance:
Brynjolffson says that capital per worker has been growing very strongly, with the gains very unevenly distributed.
Cowen says that the Solow residual per worker has been growing more slowly. More capital per worker means doing more with more. A higher Solow residual means doing more with less.
Both of these views could be true. In fact, if you were to ask me right now, I would say that they are both true. Indeed, suppose that the Commerce Department has understated the growth in capital by failing to make sufficient allowance for quality improvement. If that were true, it would strengthen both sides of the debate. It would show that we have had more capital growth, and at the same time it would show that the Solow residual is smaller.
On net, I come away from this debate with more sympathy toward Tyler's outlook than I had before.