Glazed
Legend
Daggers would be better if it was 15.74 DPS, but it isn't.
Shadowfang has the Shadow bolt which makes it better, only if it keeps procing, which it won't.
Dancing Steel and Deadly Poison have a better chance to proc on a Wingblade because you will hit your target more often within the time window you have you hit your target, making Dancing Steel's and Deadly Poison's proc % more accurate.
You have to note that offhand swings are only auto attacks, which is a 17%+ chance to miss a level 19, making the Shadowfang proc itself even less likely to make it better than the Wingblade.
Shadowfang has the Shadow bolt which makes it better, only if it keeps procing, which it won't.
Dancing Steel and Deadly Poison have a better chance to proc on a Wingblade because you will hit your target more often within the time window you have you hit your target, making Dancing Steel's and Deadly Poison's proc % more accurate.
You have to note that offhand swings are only auto attacks, which is a 17%+ chance to miss a level 19, making the Shadowfang proc itself even less likely to make it better than the Wingblade.