The results seem to point to Interactive In-Stream video to being the best format for video completion rate as MarketingCharts reports the latest research from PointRoll...
"78% of viewers completed 100% of interactive in-stream video ads, compared to 69% who completed 100% in-stream ads without interactive elements, according to results from a PointRoll study that compared campaign results from April to December 2011. By contrast, just 39% of viewers completed 100% of in-banner video ads. Interaction rates, where users specifically took an action within the ad, were also more than 3 times higher for in-stream video ads than for in-banner video ads during the period.Interactive in-stream video ads appear to be growing, too: according to the AduTube Format Index Q3 2011, they accounted for 61% of video ads served on the AdoTube Network in Q3 2011, representing a 13% rise from 54% in Q2."