I prefer binge-watching but I usually don't watch more than 3-4 episodes because it starts to get tiring. But I watch both on-going anime and completed anime. The problem with on-going anime is that you never really know if it's not very good or not and when you actually realise it it's too late whereas with completed anime since you are watching it continuously you can kind of figure out whether it suits to your tastes or not so it's easier to drop it. Plus with anime that are mystery or thrillers or even action the tension that's built up over episodes is lost if you have a gap of one week between each episode.
But I do both because sometimes I'm too lazy to go out of my way to search for a completed anime so I just catch up to whatever on-going anime I'm watching.
