Week 5 Fantasy Football Start Dilemma......?

I have to start 2 RB's and 1 Flex Player this week. I've got Larry Fitz and Brandon Marshall at Receiver, so I feel I am solid there, but I have to choose from Clinton Portis, Marshawn Lynch, Maurice Jones-Drew, Chris Johnson, and Desean Jackson to fill those three spots (2 RB's and 1 Flex).