Forte avg defense rank against run ROS is 9.4, Charles is 23.6 so that leans Charles.
I've already told you why I like Forte so I know you are looking for other input, but while the rankings may make it seem obvious, all the defenses Forte faces have been run on. Forte sees the Vikings twice who allowed a huge day to Martin, 49ers who allowed 100+ yards and a TD to a struggling Sjax, 100+ to Lynch, and 100+ plus TD for Bradshaw, GB avg giving up 16, and Ari giving up 15.5.
I think another aspect is how long Cutler is out. When Cutler is there Forte value is higher, but if Campbell is in the will load the box against Forte.
If Charles were guaranteed touches then I would go him. When he gets 15+ touches he is a beast, but some weeks he gets less than 10 carries which won't help you out at all. I don't understand why they don't feed him but until they do, I like Forte