Quote from Remeiko »
We have sub-par knight tribal commanders, no commander has all 3 colors (Abzan) to make for a solid commander. But other than that I do agree warrior tribal commander was a long time coming.
Every Knight Tribal card (of which there have been relatively few) has been either Black or White, so what's Green needed for? Just Knight of the Reliquary? Juniper Order Ranger and Knight of New Alara? Wilt-Leaf Liege?
Aryel is sufficient for Knight tribal, and there are some wackier options out there if you want. I'm partial to Edgar as a Knight tribal legend myself, since he makes Knight tokens - you can use Haakon, Stromgald Scourge to loop Crib Swap/Nameless Inversion/Blades of Velis Vel to generate Knights that then pick up whatever Knight tribal bonuses you scrape together. There's also a decent amount of natural Vampire Knights in Shadows to trigger him.