Martavis if Ben somehow plays. Crab if Ben sits.
Crabtree has played really well this year. I think his problem in SF was that he was never a true #1 WR. He does make for a really good #2 WR though. It also helps that he has a real QB throwing to him.
Keep an eye on Ben though. Apparently he has already shed his walking boot and wants to play. I still think they hold him out since their bye is next week, but he is one tough SOB.