If the weather's good, I like Denver to win big. If the weather is really bad, I like Seattle. Not sure how bad the wind gets in the new stadium, but it was almost always an issue in the old Giants stadium late in the year.
If the wind and rain/snow don't take away the passing game, I think Manning will pick Seattle apart. IMO, Denver caught a huge break in not getting SF. SF has a much better pass rush, and that's the key to stopping Manning. Their secondary is great, but Denver has too many weapons for them. And Seattle's offense, while tough and consistent, doesn't put a lot of points up usually. And it should be noted that after losing to SD, Denver needed to win the last 2 games to get homefield, and their D has been fantastic since, shutting down SD & NE offenses that had been on a roll.