A Link Between Worlds. Think it's the only game in the series that I played consistently until I beat it, rather than getting off-task and/or procrastinating. It took me a week in real time, but it actually compresses to ~20 hours when you include only the play time and exclude the sleeping and the interneting...
I recall beating Ocarina of Time 3D pretty quickly, too, but I definitely had a few more intervals of neglecting the story and dungeons in that game, so it probably wasn't as fast as my first (and only) playthrough of A Link Between Worlds.