I fly Korean Air to Toronto quite often and tried both the prestige and first (but the older style, not Kosmos).

Prestige: the seat is 170 degrees. I personally never sleep well on these seats. I feel that the slight angle is bothersome, in addition to the really thin cushions below it. Service is good, meal service is proper and the food isn't too bad. I think the mains are a little weak, but the dessert is pretty good (on YYZ-ICN). For the ICN-YYZ flight, they use the 777-200, so I'd say the bulkhead in the second business class cabin is the best. It's quiet and only has two rows, I usually sit there.

I haven't flown to Beijing on KAL in quite some time, but from what I recall, if they use the same prestige seats, they really are lame. They have so little room, but the service is consistent with their overseas flights.

First: I don't know about the new seats, but the service is really good. I can honestly say aside from the pajamas, the food and other amenities aren't that much better than business. But I've heard the Kosmos seats are wonderful.