Chiefs have the edge certainly. But the Seahawks run the ball well, which is KC's weakness, well one of them. I don't think KC will have much of an answer defensively, so it's probably going to look a lot like the Seahawks/Rams matchups of this season, where Seattle makes it an ugly game and have a chance to win it at least.
IMO the Seahawks' defensive style is a nice fit for where this league is trending, with a cover 3 approach and rangy DBs mugging receivers underneath. Defenses like theirs, as well as the cover 2 type defenses, are well suited to slowing the heavy passing game opponents who are leading the playoff field.
Seahawks are a team to take seriously I think.