I believe no one metric has the defining weight. As Katy mentions, a 100% retention rate is amazing and would offset the lesser watch time. Back in the day, when YT just switched the algorithm to watch minutes instead of retention, the game play video had a serious advantage, hence the immense growth of let's play channels and the like. However, they seem to have tweaked the algorithm for a balance of watch time and retention (relative retention is very important as well), which is demonstrated by the re-surge of animation channels (who post less often, but whom's videos are often watched fully and multiple times). So at this point, just going for views or watch time isn't enough. You need retention and interaction from your audience to be favorable to the algorithm.