Hands-down, the very best Korean restaurant was called the Korean Restaurant.
https://www.google.ca/maps/@42.98134...7i13312!8i6656
It was in a shabby part of town (Hamilton & Adelaide), but had by far the best Korean food in the city. We went once per week (helps that my wife is ethic Korean).
Now the pickings are slim for authentically good Korean food. Ozen is consistently quite good but it is trendy and too popular. Other places are inconsistent (Manna Grill, Gangnam Style, Kim Chi House, Gozen, Soo Dam, etc...plus a handful of Japanese-Korean restaurants downtown).