This one. Brad DeLong didn't, so I'll outsource that job to him.
In Penner's defense he has some reasonable points about the debt-to-GDP ratio and future crises. He is also right that some on the left are dumbing the question down. But I would say (1.) fewer than on the right, (2.) that's not a big problem with the CBPP, and (3.) that's not a problem with DeLong. Penner, I think, has a lot of legitimate thinking on long-term problems that he is too quick to pull too far into the short-term.
UPDATE: Oh, and the point about Greece was completely gratuitous. He said that at the talk I shared the other day too. I should have raised my hand, acknowledged the potential risk of high debt levels, and asked him to lay out why he thinks us ending up like Greece is more likely than us ending up like Japan.
Shoulda, woulda, coulda...