If you are a Cardinals fan, you should root for the Seahawks to win every game they play until they face the Cardinals in Week 16. Why? Because if they do, there is a decent chance that they might have clinched a playoff spot and home field advantage throughout the playoffs by then. And if they do, they will be a much easier opponent for the Cardinals, who might be fighting for a #6 seed at that time. In addition, Cardinals fans should be rooting for the 49ers to win every game they play (except for their game against Seahawks) and hopefully the Niners will clinch a wild card berth before they play Cardinals the last game of season. That scenario would be ideal for the Cardinals--and give them the best chance at securing a playoff spot since their final two games potentially could be their most difficult. But not if those two teams have nothing to play for.
Go Seahawks! Go Niners!