I have Lynch, Turner, Gore, and Forte. Who do i start?

I am in a league with 2 RB slots as well as a W/R position, so i can start 3 running backs. I'm just not sure which 3 to start this week. I figure that Forte has to be a lock, with his matchup this week. Who do i sit? I also have Warrick Dunn on the bench, but I don't think he could start with who I have. Also Should I start Chicago's defense or Philadelphia's defense. Thanks.