Cohen or Cobb .5 PPR flex

So right now I intend on starting OBJ and Demaryius Thomas for my WRs and then Fournette and CJ anderson for my RB. I intend on moving one of those 4 into my flex, but should I go with Cohen or Cobb?

I also have Martavis Bryant, Rob Kelley, Amendola, and Jamaal Charles on the bench.

Thanks foot