Who should I start this week (week 4) for D/ST. I have the Chargers @ Steelers, or Titans @ Jaguars?

I have been undecided all week, and now the Steelers are reporting that Willie Parker won't play, not sure how big of a deal that is but the Titans look a little lost on Defense so far this year. Please give me some reasons along with your advice on who to start here.