I've been watching both teams for a while.
I always thought BDD had better mechanics than most LCK mid laners, perhaps just next to Faker. He's younger and just arrived at his prime now, so we'll probably see the best of him in years to come.
I think Wolf also plays better than Gorilla, but he has been making mistakes in this tournament so he'll have to step it up. I don't doubt his capacity to do so.
The real difference is in the top lane and jungle. I know Huni is good but Khan is just superior this year. Other than that, we've seen Peanut fail to adjust to the meta champions. I doubt that SKT will play to the meta against Longzhu in the tournament if they end up playing against each other (I suspect picks like Olaf or Lee sin).
My vote is on SKT because despite their mediocre performance in the tournament, Faker and Wolf know how to turn a game around, and I haven't seen that particularly from Longzhu players.