I appreciate the question. A lot of people are worried about Jamaal Charles because he's losing significant touches to Thomas Jones. As far as big-play potential, Charles is definitely much more attractive than Tolbert, even if he gets far less touches.
McCoy looked great and with Vick at the helm, he'll have a lot of room to both run and also run after those short passes.
Hightower should be in line for majority of carries again this week, but watch out because Beanie Wells is going to make his debut as well. Coach Whiz has said Wells' carries will be limited, so I'm gonna trust him and say play Hightower.
Tolbert is the safer bet to get majority of the carries that a healthy Matthews would have had, but Sproles will pick up the passing plays most likely.
In the end, it will come down to your gut and some chance. Can JC bust off some big runs against a tough 49ers defense? I'd say he's more of a gamble, but I personally play him over Tolbert. I like high-upside. If you're the safer-bet guy, go with Tolbert.