Rashard Mendenhall Vs. Den. or Michael Crabtree vs. Tenn. as flex?

Normally, I would go with Mendenhall in a situation like this, but only the Steelers and Bengals have given up fewer rushing yds to RB than the Broncos. Meanwhile the Titans are dead last in giving up fantasy points to WRs. They've given up almost 1500 yds receiving to WRs and 15 TD receptions. Given that the 49ers are making aqn effort to get the ball to Crabtree, this is the ideal week to put him in the flex.