I used to play Sensei Yu all the time with Lynch for the push and useful actions for Disciple. The biggest reason I had for choosing Yu over the Emissary is that Yu can target Lynch with his Mighty Gust, while the Emissary's "Rite of Strength" can only target non-leaders with an upgrade.
That being said, I've since replaced Yu with Maddox, and haven't looked back since.