Offensive player flex slot: Eli Manning, Wells, and Portis

[ChopBlocker]

Instead of a flex we start a general offensive player. Usually I start Eli Manning but they play the bears and I start their defense and have no better options.

I'll either start Wells or Portis at 1 RB slot, but should I start the other over Manning this week since any points he scores will decrease my defensive points (i.e. -3 points for my defense for every 4 point TD he would throw)?